Cryptocurrency is the future of all payment method due to the decentralized nature which grants financial freedom and power to the people. However, for it to replace cash or the Fiat, it will take years of awareness creation. Up to date, some people do not have access to internet whereas others do not know how to access it.
No, Of course we still need fiat (cash) because the cryptocurrency is only a medium exchange to be a digital currency our cash. So what if all the money or fiat are gone? Where we can change our money? The other will answer my question "Of course in the exchange site" My point is what if our grandmother or grandfather doesn't know about the crypto? For example, Grandfa I will give you 50ETH so you can buy any want now. And grandfa said "What is 50ETH? Is that a new form of money?" How do we explain to them?