Cryptocurrency will take a large bite out of fiat currency yet fiat will not disappear. We are moving towards a digital world and that is where crypto will dominate. However, we still have the physical, geographic side of things and that is going to remain in fiat's realm.
In a tokenized world, everything we do will have a token attached to it. Seamless transition from one to the other (and to fiat) will mean that many different currencies will be used throughout people's days.
Fiat's monopoly is quickly coming to an end.