There are no chances of that happening.  It is not possible for cryptocurrencies to replace fiat money.  The level of illiteracy especially in developing countries is a big obstacle for cryptocurrencies to replace fiat.
Another major reason is lack of internet services in most places in the world. We are not oblivious of the fact that to deal with cryptocurrencies, we need internet services. In places where this is not provided,  it is impossible for cryptocurrencies to replace fiat.