Minfilia seems to survive as Yoshi already showed a new concept art of her, didn't he?

What I don't understand though: If Bahamut goes around rampaging without hindrance and can destroy a city in mere minutes how can there even be a world in 2.0? I mean if he is mighty enough to wipe out Eorzea and those who should stop him can't do so...then why is it logical that the cities survive? Can you build up a city STATE to such an extent when probably (almost) everyone should have fallen victim to Bahamut, not to speak of resources...
(He wasn't even close to the cities and still Bahamut damaged them severely with just one meteor shot.)
If chars like Minfilia or Gaius van Balsear (seen on the official website) survive, why do we need all this special magic and Loisoux dying...

The only thing I can imagine is that he runs out of aether, disappears hence and needs to regenerate a few years. But that on the other hand would leave Eorzea devastated as well as it needs aether to survive and if Bahamut has sucked all up... :/