A quick way to show LOCATION based tension:
You tell the player, okay, so the gang doesn't find the BlackTeeth hiding out there in their muck camps or whatever, but instead tracked them down to some other holding. This holding probably should not be buddy buddy with the players, but it's best if we'd heard about them before. Or you just introduce a new one if there's room for that in your fiction. The unled brutes don't think too hard about it, and start a battle in the middle of the market over the girl. The options outlined above, might still apply, but the always statement afterward could change too:

The hardholders favorite X (son, daughter, arms-dealer, drug-dealer, etc) was in the market that day, and died out there with a gunshot to the face. Your guys got back with the girl (if they picked that option), but the hard holder knows where they came from. Because someone else in the bloody market that day recognized them.. or maybe the BlackTeeth were hit the guards hard there, and the hostages that would have been their's are now this guy's. They flipped at the first sign of pain, barter, or whatever else. Now the Blackteeth have basically been wasted, there might be a straggler mutant/cannibal threat surviving out there somewhere, but we've changed that into a different kind of foe. In this case, I would probably not be as hard when it comes to injuries on the people that make it back. Because the focus won't be small scale violence, but the new looming intimation.

If neither side ended up with the girl, then the hardholder did by default. Now maybe he wants a second wife out all this.

Honestly, Seize by force is what you make of it. Harm can mean all sorts of narrative things too. Especially when that harm is happening off-scene like this. Sure, the play might always choose, they certainly grab her. In fact, that's not so unreasonable, even if it was a love letter, most of my love letters would also give the player a chance to say, they grab her too.

So we already determined, that if they couldn't do it, then this roll does happen. It only happens IF there is a chance that they could. I might give them a penality of -1 or -2 on the hard roll, depending on how good the chosen bunch of random followers turned into a crappy gang would fight together. I'd also certainly use the hard of the character that talked them into it for the roll.

Maybe this is only because of my hack, however. But:
10+ options:
  take definite hold: They most certainly grabbed the girl, too!
  suffer less harm: Keeps "Boxtop" alive, the Hocus's favorite, otherwise Buhbye Boxtop. I assume if the NPC's were on scene and talked into doing something, we as the players might care about one of them more than the others... I'd use this to decide if our favorite gets back at all. You also suggested that it wasn't the Hocus that talked the followers into doing this, is the Hocus really okay with it? If not, I'd push there hard.
  deal more harm: They even managed to kill one of the BlackTeeth! Pissing them off mightly, and making it harder for them to recover to the same level of dangerous. This might make the resulting snowball less threatening.
  frighten, dismay, impress: The BlackTeeth won't come back at the Followers in the night, to their homes, to their families, at their soft underbellies. Instead, they'll be more cautious in their approach, coming straight to the players with demands. If the player picked deal more harm, this violence here will be deadly. If the gang didn't deal additional harm, then they went to use their hostages to demand from the people that loved/needed them, terrifying the shit out of them, maybe burning something along the way. This prompts an even more drastic response to the always statement.

  always: the harm being inflicted here is substantial to that group of 5. 2 or 3 is not a small chunk. What happens when they're caught? What value did they bring to the community that's now gone? When the BlackTeeth use them as hostages... who might care? If they really were nameless and expendable, I'd change that immediately by bringing in those NPC's who cared about them in some way, or who relied on them to survive. I'd bring them right up in the Hocus's face in an unignorably pleading or angry sort of way. I'd probably, as I always do when people choose to inflict extra harm, add casualties to the conflict that maybe aren't always moral. Like the followers ended up killing some of the kids there too, or wives, or the favorite son of the gang, or bystanders got shot. Unled brute Harm has been dealt Dealt.

7-9 options: (same as above but, the NPCs get to pick one if the player doesn't cancel it out)
  NPC's choices...
  frighten, dismay, impress: The Followers that went come back Freaking out, with a capital F. They're literally balls to the walls terrified. They wish they had never done this, they might even act out against those that talked them into it. Of those that returned, they're not the same. I'd go as far to say I'd change their threat type, maybe already delivering some additional trauma in a counter attack where the NPC's were weak (home, family, etc). Maybe even have one or both of them leave the cult entirely, or demand recompense, depending on the setup. One thing's for sure, those guys will never do something like that again.
  deal more harm: Okay 4 harm? If the player lets this happen, every single one of them has been at least shot or stabbed. One of the two of them who would have made it back died out there instead. This should snowball, I'd certainly snowball part of that into a bleeding (shot or stabbed) pregnant girl.
  suffer less harm: Okay, so the BlackTeeth didn't even get hurt. I'd only consider this if the player didn't select deal more harm, because then I've got a full-health gang coming back at them, or chasing them on their heels. I might go as far to say, that when they show up with the girl, they show up still in the middle of that battle, they've just brought it all the way here to the PCs, except they brought it on them in a place that isn't good for the PCs. Maybe at night, maybe sideways, maybe through or into something else that shouldn't get all shot to hell. Dunno.
  take definite hold: If the player didn't choose to take the girl, this would be they barricade themselves up tightly with her now. Maybe they make her theirs, or as was mentioned before, she makes them hers--but turns out that she didn't really want to get "kidnapped" back to the Hocus anyway. If the player did choose to definitely grab the girl, the NPC's could counter that neither group has her, she got lost somewhere in between with all the fighting and when the followers come running up screaming to the PCs for help... Now she's not in anyone's hands is even MORE dangerous. Now the story snowballs sideways because she's far more likely to get kidnapped by something worse out there alone, and far more likely to get shot by competing interests, fighting over her on whatever's been turned into the battlefield. This is also true if neither side picked to definitely grab the girl.

On a Miss: (same as above, but worse)
Okay so in my hack, the NPC's now get 3 choices (or 2 if the Blackteeth arent really all that), and the player gets 1. So that always makes the situation worse.


No matter what: We solved something with violence, and it was done off-scene with brutes. That means there is a fucking mess on our hands. That is snowballing for sure, and this snowball I'd probably have moved to either immediately on the scene, or into a love letter for partial resolution. The followers that started the fight will always suffer enough harm to break, so they're not helpful at all in what comes next. What comes next is most certainly a violent or hostile response of some kind. The battle isn't over, there is just an intermission.

Actually, I think the character being peeved at the disappearance is a good use of the move. I would not just say, Oh you can follow them down the hatch! Or any other sort of the maelstrom will let you do it-isms, unless they pushed that point themselves, then maybe.

Nothing wrong with one character abandoning another weirdly. That is good story too.

I want the Savvyhead to roll at the start, because I might want to put him into the sitch. It's not only his call how bonefeel works or when it fires.

Concurrency between scenes isn't something I have to deal with much. I normally run a scene all the way through, so Bonefeel wouldn't pull someone out of something, it would merely put them into whatever is currently happening, right now. That's not true in every case, but, most of the time my players are as interested in maintaining the logical flow of the story as I am. Ninja vanish is not what the move is called, but...

In one of my favorite (one-shot) games, Bonefeel was a straight up teleportation due to an apocalypse where the spatial and physical laws were being destroyed. I mean, entire buildings could fall into other parts of the world, and waterfalls and rubble would just spontaneously erupt from the sky. In that type of game, I would be like SURE! We can definitely hop scenes!

However, it happens that if the player can pull a character out of the middle of another scene, so can the MC. Nothing like the Savvyhead running up to do something critical, and then suddenly being dropped into another characters gunfight... leaving both groups up shits creek. That's a sweet level of narrative, actually, but I'm not so sure that the Player will think this move is a huge perk if they can be interrupted by space/time because they banked the hold for to long. Still, yes, huge fan if everyone wants to do it that way.

I often use a combination of open your brain answers and love letters to handle "flashback" scenarios. Love letters can come in with built-in questions and bullets to charge the answers, so I tend to prefer this. Other times I just look at the player and ask just after a backloaded prompt (like Munin's example).

Without going into too much detail, what I was apprehensive about was it could trivialize certain events by just being way to powerful. What worked out really well was the fact that the others around the table didn't just endorse the addiction and strangeness: Some tried to stop it, some tried to direct it. It added both an incredibly personal story to the development of the maelstrom, while at the same time allowed a bad-guy type of vibe from the players that felt uncontrolled, and therefore less personally aggressive. Some people don't like it when another guy at the table shoots some NPC they care about, and if it happens a few times, they might take it personally. In this case, the contamination was really the thing in control, and it really brought the threat home to the group. 

It's like when we did barter in AW1, people really didn't use barter very much, it was almost a background living expense or a plot device. Either way the players didn't struggle themselves, so the suffering was a step removed. In this case, it really took the threats in the world, a disease crippling a people, a strangeness of drug-addiction clawing its way through... and brought that into the game in the same way. Suddenly the PC's were personally confronted with a contamination that was fun enough to have around, but in the same way, was corrupting them and their agendas.

All that said, I probably won't be running a full game with the playbook in the immediate future, I just wanted to try it out, and then give some feedback. I have a long-running game atm and won't be seeing this until the next one rolls around probably.

I've handled that go aggro situation a much like hobbesque. I tell my players, you know, sometimes your character just isn't as Hard as you want them to be. And so when you choose to go aggro, if you hit a 7-9 and they're backing off, you cannot just shoot them. It's not in your hands, you're just not hard enough to follow through. Generally, though, them backing off comes with words that tend to disarm the violence as well, so I've never had a player even raise a concern about this.

I have also done things similar to Munin's reaction there as well, so long as the NPC didn't get to draw and also start blasting, that's fine by me.