If they can do that then the market will thrive on its own and create more business opportunities. I do not care about what China or any other country say about the cryptocurrency market, all they can do if they really want innovation is to leave the market alone.
So they are in a difficult position, if they do nothing as you suggest then this market could grow to the point it replaces their fiat currencies, but if they do something and they fail then this will show how incompetent they are and how there is no way for them to stop this market despite their best efforts.