I bilieve that in the future crypto currency will not replace fiat money as mode of payments in the future. Why? Because this two currency have a unique combinations that make our life more secure and convenient transactions trough offline and online transactions.
1.Crypto currency is more secure and faster transactions than fiat money via long distance and transactions like sending money around the world crypto is fast, safe and more secure then fiat money in this case fiat money is not good and slow in long distance transactions.
2.Fiat money is more faster and more easier in hand to hanp, face to face transactions and offline transactions in this setuation crypto currency is not good.
This 2 reasons why crypto currency and fiat money will be a powerfull combination in the future.
Fiat money is unfair, you can see the result of fiat money usage now that is inflation. Even some of fiat money become worthless because of money trading. You can see bolivar as the example of this cases. My point of view is that fiat money will be dissapear/unused then it will be replaced by gold or bitcoin (virtual gold). But I prefer gold as money. No good combination between cryptocurrency and fiat because I think both are the enemy of each other. Cryptocurrency and gold is the real best combination because the amount of bitcoin is always same and gold too.