Cryptocurrency replacing fiat isn't that easy, to experience a complete usage of cryptocurrency same as the fiat it needs a large scale adoption. Compared to the previous year what we experienced by this year is a massive fall, but adoption has been taking place in a gradual manner. With this I believe, in future can experience cryptocurrency usage same as fiat but replacement won't happen.
I think if the states will come to enter in this field then it will not be hard for the crypto to replace the fiat. Right now it is hard because the states are supporting their fiat and for the ordinary people it is impossible to compete these states.