Fiat will be replaced by crypto currency but i dont think it will be bitcoin. Government want to control everything and even fiat money , bitcoin cant control by the governement so they will create thier own and will use blockchain technology to make a new way of payment before fiat currency fall.
The government will just end up adopting cryptocurrency in the future but instead of adopting existing decentralized crypto like bitcoin who is really dominating the crypto market, they'll just create their own. That's a very obvious move by the government. They won't allow decentralized to dominate on their country so they will just make their own cryptocurrency where they can still control it