If this is their bread and butter or even they get lots of benefits for using crypto for sure that people will continue to use this.
But if it happens that they are not a regular crypto user and they are just here try their luck to earn then this people would possibly avoid using crypto if there's ruling that government will think about crypto is illegal and put penalties to those people who use it. Also provably common answer towards the question is depends on the benefits what people could get on crypto since this is deciding factor to them to stay or obey then quit.
I think some can still quit because they are afraid of the consequences and then maybe they already save enough money to start on a new journey? I'm talking about the people who deal with legal stuffs because those who aren't have no fear and they are used to it already.
For those irregulars, there are also some that are willing to take risks. This is the same to those who bet on underground matches. Irregulars exist though even on a normal market condition. So the answer to the OP's question is no, the cryptocurrency market can never drop to zero but obviously it can be affected greatly if more or all countries will turn against crypto.