Possibly yes in the near future but not entirely. Fiat I think would still be the main currency in the coming decade or more though I think other currencies would be accepted, especially bitcoin as some countries are already supporting this right now. But for the question if it can actually replace the current monetary system? I don't think I'd be able to see that in my lifetime
I don't think bitcoin will be able to replace money, from the amount itself, bitcoin won't be able to support half of the world wealth, and then for now the transaction speed still become number one problem why some store doesn't want to use bitcoin, so I don't think bitcoin can replace money
The number of Bitcoins in circulation is enough. If all the people in the world converts all their fiat into Bitcoin, it will just inflate Bitcoins. Bitcoin doesn't have to be billions in number in order to support the wealth of the world. Actually, even if the number of Bitcoins in circulation is lower, it would still be okay because as more people convert their fiat into Bitcoins, it will just continue increasing its value.