I think fiat money will always be used even though crypto dominance continues to grow, the fact is that some regions do not fully have the same level of technological progress, even in some places, the distribution of internet facilities has not been evenly distributed.
Another reason is that the government cannot fully trust the decentralization system, this will make the national economy out of control.
no one could replace fiat money with any cryptocurrency or others.fiat backed by gold , so this is not fiat value represent gold value too.although we know too, for each bitcoin need high cost to mining.