Sure, fiat currencies will remain with us for quite a while yet. But their value will drop in relation to real deflationary money, such as precious metals and cryptos.

Moreover, fiat currencies will continue to be used, but primarily for smaller transactions. But even for such payments, cryptos might surpass fiat currency. In fact, already in China, most people do not carry any cash. All payments are made electronically. That will make it so much easier for cryptos to replace fiat.