I personally do not believe the cash will be replaced by whatever the crypto, although I hope to be mistaken.
The crypto are more to be a value reserve, as are gold or stock markets.
Why do you think so? Cryptocurrency has all the preconditions to replace fiat money.
Really? Would you like to receive your salary in BTC and find the next morning it just suffered a devaluation of 20% overnight?
Whether we like it or not, fiat will keep playing a major role in our lives due to it's stability.
Cryptos are becoming more and more attractive has commodities to invest in instead of leaving the money in the bank.
But I don't see how I can pay my groceries with crypto unstable has it is.