Yes, if the weapon is of no threat to the dragon(as in mundane weapons), then no H & S is triggered. They just swing their weapon, it clangs off of the dragon like a knife on an armored tank.(that's only if the dragon has a trait that gives it such, "inch thick metal hide" for example. Which the normal dragon doesn't have, but the apocalypse dragon does. So maybe the larger dragons. Or a special dragon devised by the DM. Or if DM decides, all dragons in his setting.

I don't remember seeing in any stat blocks where the breath attack kills instantly. It's more likely a descriptive narrative by the DM. They breath the elements. So if they breath fire, make things and people catch fire(after defy danger of course).

The DM, not the stat block created by the authors, decide what the creatures in their games can do. But you should describe it in your stat block. Maybe some dragons have supple scales and normal weapons can hurt them, but the are fast and agile. Others are like tanks. It's really up to the DM.

I personally think a catapult would be sufficient to damage a dragon, but the dragon still gets armor. And that would be an awefully stupid dragon to just sit there and let a slow cumbersome catapult hit them.

my 2 cents anyway.

Thanks noclue, that helps. Much appreciated clarification.

Seems to me that each action has a possible consequence. So if the person rolling is willing to accept responsibility for the consequence from failing a roll that may or may not benefit the entire group, then that is his choice. If he is using group resources, he must have had permission to spend it throwing a party right? Maybe not. Sure he may get the XP, but maybe things got out of hand and he is responsible for damages, or thrown in jail, or banned from town.
The fiction would also be the main concern here. Who is more likely to carouse in town? The fighter? The thief? The druid? Ranger? Bard?
Also, if someone is aiding the original carouser, doesn't he also stand his own chance at failure? And maybe if he does fail his consequence is linked to the trouble makers.
Just some thoughts. I haven't actually gotten to play this awesome game yet and am hoping I can get my players as excited as I am to play it. I have been a role player for going on 32 years off and on, and it seems I have strayed far from my role playing roots and am now just a gamer. I don't want to be a gamer, I want to role play like I used to. This game will help me do that, even if I have to drag my players kicking and screaming. And they protest too much, I will have to find replacements. Love all of the advice on these boards BTW and love the newbie guide, helped a ton.