I think It won't happen if the government doesn't go bankrupt. In other words, cryptocurrency can be used in under developed countries instead of a bank.
There is no way government can go bankrupt and even if they dont go bankrupt, the percentage of crypto usage to cash will be higher which will make bank relevance to be less but not completely wiped.
Crypto is both useful in both developed country and under developed country and to me, I think it is even more useful in developed countries, under developed countries are not much exposed to technology and for crypto to function very well, it requires technologies to be put in place, and I think banks will even be more useful in under developed countries than the developed ones.