Bitcoin could replace the money but its from now real far a way if you ask me, due to the reason the bitcoin has to get a lot bigger if this would happen. I think with the future of the bitcoin is possible but it will take a couple of years maybe even more something near the 10 years.
Even if bitcoin gets more popular and bigger in future its unlike to see that it can ever replace a paper money which has support from the Government and the society and bitcoin will be always used as an secondary currency.
I also think about it, If in future, bitcoin would be popular more, than no chance to replace the bitcoin into money, because now bitcoin is already going well, So we can guess in the coming time, bitcoin might be achieve more popularity than the countries who made the bitcoin they never want to change the bitcoin into paper money.
I don't see any instance in the future that it will happen, paper money will remain popular than bitcoin because you cannot force all the people to use computer just to transact, we want instant and simple way to transact and only paper money can provide that on us.
The world would be better if we are using both.