Sure, whole countries would be in chaos... but only for a few days, I think. FB isn't doing anything original anymore. There's tons of clones and some are markedly better.
Yea, maybe a few businesses would fail, maybe some people would lose contact with old friends. But if fb is the only way you keep in contact with someone, do you really care about them?
Cost benefit analysis is easy to do, actually pulling the trigger is hard.