It is said that bitcoin will destroy the fiat system but i believe that if this happens the world will change completly because banks and a lot of things will go out of market.
I don't think so, 2022 is just 6 years away from now. Bitcoin users well, increasing every year but I do not think that would be enough to say that bitcoin would be used by everyone. Some people especially who are older and not familiar with computers would not let go of the usage of fiat. It is more easy to use and of course it is realistic.
We can let go of the old ones with their fiat money. The important thing is we teach the young ones with bitcoin. They are the future, so if we influence and educate them about bitcoin, we are ensuring that bitcoin will survive in the future. And it might be even everyone is using bitcoin in then future. But you are right, 2022 is too near for that.