In the old age,few centuries ago people uses some money system which is called Barter system to buy and sell their products.This system works like exchanging their products between two people when they are in need but they realized that that system has flaws and not suitable for everyone since if there is no demand for one's product he can't buy anything he needs so later they moved to currencies (paper money) until now people uses this as their main form of payment but in digital format but people needs to understand that this also has flaw of centralization so we need to move to the decentralized money for better life.Lets get update ourselves to use the crypto currencies.
Some people act like centralization is absolutely necessary for the survival of the economy - it really is not. We've seen economies survive and arguably do better off with decentralized forms of money compared to fiat with no backing, or at least with less financial trouble and swings.
However even with that said and my confidence in bitcoin as an asset that is able to preserve value in the long run, it's very unlikely that governments would be willing to give up control of their sovereign fiat currencies and stop issuing them altogether.
The most realistic outcome in my opinion in terms of mass adoption is that people see bitcoin as an alternative, or parallel to the fiat banking system. Some may even choose to use it exclusively as people already are doing now. But a decentralized crypto completely replacing fiat seems like a far fetched idea for now.