I think there would be no future for paper money . if there's an future then it always use as paper money and physical money to buy some things that we need to. in daily life and paper money will never disappear right as long as we are using bitcoin then there would be a paper money to use too.
We have been using paper money ever since, and we have the best experience so far over the other forms of payment. With paper money we can transact anywhere we want to and that makes it very simple, so people will not surrender paper money for bitcoin.
Yeah even if bitcoin becomes huge in future there will be many people who will go with only paper money as they are used to it and the fact is there is no hassle in using it as it is accepted everywhere.