GlassJaw
Hero
This is a very good premise for a fantasy post apocalypse setting.
That's exactly what I'm going for.
Good stuff so far everyone! Let me clarify a few things:
What if you replaced the word dragon with "really big, vicious lizard-type creatures"? The dragons don't need to behave exactly as written. In fact, I was thinking that would be much less intelligence (at least the vast majority of them).
Also, whatever caused them to return or multiply also controls them in some way so they don't attack each other. They don't necessarily cooperate with each other though.
It's almost as if the dragons have been corrupted in some way. Not exactly mindless undead but certainly not the intelligent creatures they once were.