20 years ago nobody would believe there will be something called digital currency (cryptocurrency) that will be threatening the very existence of fiat, same thing happened years back before the advent of fiat, most of the medium of exchange back then where slowly replaced with fiat.
Now with the technological advancement of this generation it is very likely something more advanced will be created, the world is evolving very fast, new inventions every now and then, so it is possible something new will replace crypto in the future.
There were digital currencies even 20 years ago. I mean they weren't as big as bitcoin but that is mainly because of blockchain, bitcoin became the digital currency everyone accepted because of the backing technology it had with blockchain. So, everyone who worked on such projects knew that one day it would happen, didn't know when and didn't know how it would happen but they knew that it would one day be perfected and happen.
The first ever happened in 90's, we are in 2022, that is over 30 years of trial and error until this day, but if we look at 2008-2009 period as the start, that was a decade of studies done on how to perfect it as well.
Crypto has not really fulfill that aim of serving as money so far and perhaps it may or may not (it is under probability) because the future is not certain and it is possible that some group of people are already exploring something new and different using all the loopholes of crypto or btc as a case study.
There is always a possibility as long as human exist.