Personally, I will never see this happen. Crypto will exist but fiat will exist as well. They will co-exist because they have different features.
We both need fiat and crypto. In my opinion, we can reap the benefits of both crypto and fiat so why any of the two should disappear?
in my opinion, everything can happen and everything is possible if the development of technology and the development of the era requires currencies that are the same as cryptocurrencies, surely fiat currencies will be replaced
There are certain things that do not change and stay as it is and in my opinion, fiat cannot be replaced worldwide however it could be replaced by cryptocurrency on regional level. This reminds me of countries like Venezuela and Brazil where we have witnessed the presence of fiat in its vanishing phase and people in Venezuela now use cryptocurrency and there is possibility that the government might even form their central bank for crypto as well. Their demand for fiat vanished completely due to inflation.