People will still need to fly from A to B, and for many A's and B's UA will still be the only nonstop option available. They'll simply cut capacity, furlough crews, and increase award availability as necessary. Only if that doesn't help, they may consider (just consider) slightly lowering fares here and there. That way, a crisis would really have to last several months - which is extremely unlikely - to bring UA even remotely close to the brink of collapse. And then there will still be government aid, Chapter 11, etc.

Consider this a good exercise for the next recession.