First, there are firearms that withstand over 100,000 rounds (Glock, Kreighoff, some Brownings), but, who cares? I hope we can all agree that for hunting purposes 100,000 rounds is a meaningless number. If I hunted carefully and in the right terrain I could probably feed myself for the rest of my life (lets say 50 years) by firing no more than 1,200 rounds. That'd be one large game animal a month for 50 years. Any reasonably quality firearm can withstand that. Let's say instead I had to fire 12,000 rounds, 10 rounds per month, any reasonable firearm could withstand that as well.

That said, if you want to use a BB gun for survival purposes, do it, don't let me stop you (after all in I'd consider going w/o any sort of gun at all).