So during the quest "Revealing the Unseen", when I go to talk to the archmage, and there is the explosion with arcano, the archmages body appears outside like it is supposed to (I think, that's how it was in a video I saw), but there was nobody outside to prompt the "containment" quest (I think that's what it's called). So now, everyone just walks around like nothing happened. I've reloaded a previous save, and it did the same thing. Anything I can do? I'm on 360 btw.

Try reloading a previous save is all the advice I know to give.

You could try travelling to another city and back again and see if that 'resets' it.
Good luck