It's really just going to depend on how harsh the consequences will be when caught, and how deep the authorities are actually digging into catching the illegal crypto users.
What if all of the world's countries turn against crypto (which is very unlikely atm)? Will market prices go all the way to $0?
You don't underestimate the cypherpunk movement lol.
Of course it can be done if they want because the government has the authority to do so and with the consequences of very severe penalties, there is a possibility that investors who use it will be afraid. However, that will not stop some people or investors from still being able to use it or invest because they will find loopholes in any way so they can still use it. Because Bitcoin will be profitable for those who use it, many people will continue to use it regardless of how strict the ban is. Bitcoin is the same as alcoholic beverages or other drugs if it is really banned, even though it is strictly prohibited, many people still use it.