Paper money will stay forever.
Why? Because its easier to make than coins.
Right, fiat never replaced by any crypto-currency. Paper money is very important in poor people, this people want paper money to buy and use for business. Even if bitcoin become demands, fiat never fall. It will stay forever in this world.
Fiat is user friendly and legal, crypto currency only serves a limited number of people due to its limitation.
It's an online payment system or currency, but it does not have the same elements of a real money which can be use
for offline and online transation and provides security.