I think it's very unlikely that crypto will replace fiat currency, fiat is easier to use as a payment medium and also has a more stable value. I am more confident that crypto will be used as an asset.
I think every country might also change the existing fiat into digital in the coming years if the existing crypto market will be more popular than before.
I think there is a possibility that it could happen in the near future but certainly not at this early stage. Each country has its own fiat currency which represents the economy of a particular country and is visible to people they can hold as their own.