FIAT money is our daily currency which has been existing here for hundreds of years, when crypto currencies like Bitcoin is squeezing their way up to become a world currency and sort. Can they co-exist? If so then what benefits we can get from them, altogether? Not separately.
Of course they can and right now they do. Fiat can stand with out bitcoin but bitcoin with out fiat what would be the value? To which currency will they base bitcoin price with gold? And gold value will be based on what? I cannot imagine bitcoins fate if there will be no fiat.