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?
Your opinion that you convey is very true, but everything can happen all the time along with the development and technology, of course, because currently no one can predict for sure the development of crypto currencies.