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 too, believe in what you have believe fellow. It is true that crypto currency will not replace fiat. We feel more secure if the cash is in our hands or if things are tangible as compared to intangible.