Fiat currency, hard cash, and some other stuff will become a thing of the past! I think we can start counting years before they totally disappear. The only place where you will be able to see cash will be a museum! 30 years ago we didn't have E-games word championships, crypto-currencies, the internet was not developed as it's now. We are moving forward and I think one of the next steps is having global internet money (that will be crypto)
and everything will be global and crypto!
Undoubtedly, in a certain future, cryptocurrencies will replace fiat paper money, but before this happens, an average of 2 generations should change. We know that the world's population is largely composed of elderly people who in no way want to learn how to use cryptocurrency in everyday life. In addition, today we need very good knowledge in order to be able to and know How to Save your personal funds in cryptocurrency equivalent.
Honestly, crypto have the potential to be the mainstream of payment in the future but it cant replace fiat currency and if you read the concept of bitcoin with the message posted by Satoshi you'll understand that crypto was created as an alternative solution to what fiat currency cannot do and not to replace it. Besides, the government wont allow that to happen.