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?
I agree with this since we cannot force everyone to be involved in this community if they dont see the potential that this may happened within their systems and I think will cut the idea of making this crysptoccurency which we called Bitcoin as a universal currency of fiat, due to the fact that not everyone has the capability to accept this in their country which lead them to banned bitcoin.