Even if cryptocurrencies weren't completely stomped out, shouting "Bitcoin lives!" from a prison cell wouldn't be that helpful to the person serving the sentence. The "many-headed hydra" isn't much use to the severed heads.
Moreover I don't think the failure of the "War on Drugs" provides a relevant example. The inability of the government to stamp out illegal drugs doesn't indicate that it would be a reasonable risk for many (or most) people to maintain their wealth in cryptocurrencies, if cryptocurrencies were to become illegal.