I have a guess about how Age of Ultron can really be happening and yet NOT have the Marvel Universe being in a post-apocalyptic future to come--without altering the fabric of reality. I'm not posting this anywhere, other than telling you, so as not to spoil it for other readers: I think it might be happening in some sort of Matrix-like virtual reality. Everyone could still deal with the after-effects of the trauma, but without everyone being dead, civilization/infrastructure destroyed, etc.
It could be that, yes–except that it isn’t.