That would be a chaos if it happens. There will be wide-spread panic everywhere and people would rush to have their bitcoins moved and turned into fiat. These people are the weak-holders. The only people that will be left are those who believe in the core of bitcoin. Aside the weak-holders, the other group of people who I think will vanish if countries banned crypto exchanges together are those who are constantly speculating on what the price of bitcoin will be next.

But as the numbers reduce so will its price ultimately. But is not going to happen, that is too much of a dark thought to have. Even thinking about it is sad.