First, adressing the 'Mistake Potential', it's not like that. The Harm rolls are still harm, both the Protection and Damage. So, when you fail in a Protection roll, you will receive some kind of physical, concrete damage. You may be pushed back, grabbed, desarmed, asfixiated, mutilated, scratched, but it will be damage. So, HP could be renamed, but it should be something like 'Life', 'Fortitude', 'Energy' or something like that. HP is so common in rpgs that it's automatically related to life, so I see no use for changing it. Even so, as it's the nature of Aw, you can change the name with no problem. You can make it just like what you want, no worries about that.
Now, in regards to the 'lethality' of the system, just like in DW you can make things last as long or as little as you want, here you can make the damage be brutal or not. For me, even more than the normal damage rolls, this proves to be more related to story. A narrative damage works better for me than a mechancial one.
So, how to adress the problem? One thing you can do is having special moves for the damage roll. So, for example, for tough monsters you could say they only are damages in a 10+, instead of a 7 to 9, while weak monsters are scratched in a 6-, mutilated in a 7 to 9 and completely obliterated in a 10+.
I, personally, dislike that. I prefere the 'one table to rule them all' way. A 6- is no damage, a 7 to 9 is a fleshwound, a dizzyng blow, and a 10+ is a serious wound. What I do, instead of having different effects for different monsters, I use the idea of critical damage, which I explained in the Dark Souls hack of mine. The idea is: Every damage may have a special tag (like Sharp, Fire, Cold, Acid, Poison, Curse, Demon, Radiant, Cold Iron) and, if you are hurt with a special tag and your armor doesn't have that tag in it's protection, so you will receive critical damage.
When you receive critical damage, if you take 10+ in your protection, you count as taking 7 to 9. That means that you will get hurt no matter what you roll. That, in the fiction, is the elemental magical damage going through your armor. It's the breath of the dragon going through the armor, or the bilefull nature of the otyugh poisoning you. This works the same for players! When they do critical damage, if they roll 6-, they count as 7 to 9.
And what about death? Well, what I do with the narrated damage, instead of the marks of Scratches, Wounds and Lethal, is just to consider a soft damage (7 to 9) be a preapartion for a hard damage (6-). In other words, it's just like the idea of Soft and Hard moves. When the monster hits you and you roll your protection with an 8, you may be grabed, pushed back, scratched and, in the next action, if you do not recover from it, the damage becames Hard. It's like having one extra Hard move for the MC, which titles:
. Escalate a soft damage to a hard damage.
And how could you deal with a hard damage? There are some interesting ways. In the Monster of the Week rpg, there is a box that you can check when you are 'unstabilized'. You can have that in the game. When you roll 6-, or, by other means, receive a hard damage, you mark the box. That means that the damage you received is lethal and, if not stabilized, it will kill you (it's only getting worst).
One new idea I had is to use similar moves as the Madness moves for Dark Worlds (the Cthulhu Dark AW hack from Thievves of time). When you get mad in that game, you can make 'mad moves' so you can reverse back to 'sane'. Well, when your are hurt, you could make a 'Heal move' to be back in active.
I think that could work with Soft Damage. It could be like this:
When you receive Soft damage and want to recover, you can:
. Try to push away or problems or strenghten your musculature (roll+Str); Try to roll away from danger (roll+Dex); Try to recompose yourself (roll+Con); Try to ignore pain and focus (roll+Int); Try to have faith and tune in your instincts (roll+Wis); Try to have courage and good will (roll+Cha).
. On a 10+, you are recovered. On a 7 to 9, you are recovered, but a complication arises (like in the move Defy Danger).
The idea is, when you receive soft damage, you are in a hard spot and, if you do not recover, you will be getting damaged hard. And to heal from hard damage, you will have to get medical or magical treatment.
What do you think?