For now bitcoin replacing money is impossible. It is also impossible in the near future since banks and governments will take actions to stop bitcoin for replacing fiat. In the far future, it might be possible that bitcoin replaces fiat if and only the government officials or leaders at that time supports bitcoin and will allow it to be used as a currency. There's a low probability of it happening but at least there's a little chance that it might happen. 
And I think that FOR NOW will be bound for forever. Frankly speaking, digital transactions is always benefiting those who has access in digital world. How about those people who can't touch even google.com.
Well the odds is really low for that to happen.
Exactly and people who don't have access to internet will never be able to use bitcoin and for them paper money is the one and only thing to spend their money so I think paper money will always survive.