Do not worry about it as it is in the next 10-20 years. Money continues to be circulated as a single currency accepted as a common payment method.
I think that money will be used for the next 20-50 years. For countries with a backward economy, it will be difficult to change money for crypto currency.
That is not true because i watched a video in facebook that is telling about the Zimbabwe going into cashless and that is almost the same with using cryptocurrencies because you don't need a fiat or physical money anymore because you can just depend and be full force in cryptocurrencies as a daily basis currency and many more things that you can get benefit in crypto.