These countries or other countries that have had their Fiat devalued to the extent it is looked as worthless would not abandon their currency because of the role that money plays in the system. If you Google that information about the role of money, you are likely to get these:
Unit of account, medium of exchange and store of value

That means the Zimbabwe currency or that of Venezuela has those functions still. Most importantly, they are used for exchange and whichever that will replace it has to play that role effectively and I don't think bitcoin or cryptocurrency has taken that spot yet in such less developed countries that are still considered high in the level of illiteracy.

I have to also add from my view that Fiat is a unifying model for the econony and identity , where government runs on digital currency at most, it still will not take the place of Fiat/paper money.