The thing is that fiat is already available in digital form (via credit cards, debit cards, etc.) and has been for quite a while now. Most fiat is just numbers in a computer. Sure, crypto may handle that a lot more elegantly but from an end users point of view that hardly matters (for most anyway). The other advantage of fiat is the ability to transact with physical money. I know a lot of people think that will go away and that seems to be in the direction we are ultimately headed but I think it will be a long time before the need and desire for physical money goes away completely. If governments yank physical money any time soon then people will be transacting in silver and gold again.

Crypto is incredibly useful and I don't think it is going anywhere but it has a very long and difficult road to travel to replace fiat completely.