Yeah, Hastert's comment was pretty stupid.
If you look at this picture of the New Orleans Skyline you can see that there's an awful lot of modern, commercial high-rises and skyscrapers, just like in any other American city. Granted, the windows were probably blown out and they sustained quite a bit of damage. But chances are, they're all probably still structurally sound and will NOT be simply abandoned.
The structures may be sound but there will be problems with mold. Any place that is somewhat warm and damp will have problems with mold. Let it set for several months and you will have an extreme problem.