Oh, they'll rust down for sure, and you might have to watch yourself on staircases, but they'll stay standing a good while. There's also (or at least when I worked on them) a ton of paint and primer and stuff already stored on board, so it should be easy enough to maintain a living section while letting the rest of the rig rot. But yeah, not a multi-generational living situation for sure. Hopefully the zombies rot away before the rig does.