Banks you mean, not government because it was the banks that issued fiats but if there will be no banks, the government will have no choice but to use cryptos as a primary currency. I think it's not about the control but it's about the complications if there will be no fiats but there's only cryptos.
Even myself I can't imagine the world will be after that. El Salvador only adopted bitcoin as legal tender but is it written in the law that once the country made cryptos a legal tender, fiats are now be eliminated? I guess no because el salvador still have their fiat. In the next 10 years, maybe we have lots of countries that made cryptos as a legal tender. That's still nice.
As long as banks exist, Fiat won't be going anywhere. It's unlikely governments will ditch Fiat in favor of something they can't control whatsoever. Centralization will always be with us, no matter how much we hate it. I'm fine with that as long as people have a choice from one type of currency from the other. In the future, both crypto and Fiat will co-exist as mediums of exchange anyone can use depending on their needs.
Within just 10 years from now, a lot of improvements will happen in the crypto/Blockchain space. I'm pretty sure crypto will be much faster and cheaper to use than ever before. Ultimately, it's all about decentralization. As long as decentralization is preserved, crypto will last a lifetime. Just my opinion