At present, the daily use of fiat currency to pay more than the use of cryptocurrency to pay. People are still accustomed to using legal currency for payment. In the future, the government may issue its own digital currency, and the legal currency will not disappear.
If we take a step towards adoption, we will be able to completely eradicate the use of fiat but given that banks and other financial institutions has interests that's going to be gone when fiat is eradicated, to be honest I think it's quite an impossible feat given that the influence of these institutions are so big that trying to fight them head on will be a losing battle. Fiat will be gone if we support politicians and law makers that have principles and can't be bought by money.