Bitcoin is never going to replace money because it is going to be different from country because it would not be possible for Bitcoin to take over all currencies.
Maybe that it will take over a currency from a certain country but I think that it is not going to happen.
We don't know what is going to happen in the future but if we are going to base on our modern era. There are many billionaires that are preferring to use money which has been digitized and bitcoin is good to count and consider with it. So I think that is possible in the future but that is not possible to happen in this days.
Well, there is no impossible things that would happen as this world changes from time to time, we do not know the future so there is possibility but what we are talking here is the chances and I believe the chances to make that happen is very low.
How can a limited type of currency be circulated all around the world? 21000000 ain't enough for all of us. And the rich ones will take advantage of it and will hoard it for its price to increase. The government will take certain steps of precautions before that will ever happen. There are bad scenarios that will happen if you think that bitcoin will ever replace fiat money.