Cryptocurrency cannot replace the fiat money because of it's all where started. Both of them are different from each other but they share the same goal because it can be used to buy things, assets and more. Cryptocurrency cannot be touch or doesn't have a physical value you can only see it through a screen of your smartphone/monitor or market chart but you can use it to purchase things online. Cryptocurrency will last forever and it will be part of the economic system in each country in the world, but it cannot replace the real money.