The future of paper money is fully secured and established.It cannot disapper in the future.The daily transactions in the world are done by paper money.The illiterate and common man still use paper money for daily livings.Banks also give us paper money for loans.They do not pay us in cryptocurrencies as they do not have any control on cryptocurrencies.Many nations still do not know about the cryptocurrencies and cash is the only way.Cryptocurrencies are also in demand but it will it take many decades for them to compete with the paper money or fiat money.
It is true that the future of paper money is fully secured. It is also true that the fiat currency will never be replaced by the digital currencies. I believe that people will not easily adapt the digital currency.