Paper money will stay forever.
Why? Because its easier to make than coins.
The paper money will exist forever because no matter how many bitcoin we have keep in our wallet in the end we will convert it into cash. Many people around the globe dont know how to use bitcoin and they dont know how it works especially the uneducated or the poor who not even know how to use computer for digital transactions.
For a longer time maybe but not forever, this world will change and we are going to live a more faster life because of the convenience the technology has brought. Innovation after innovation will happen and if we do not want to be left behind we need to adopt, it will not happen abruptly but slowly the world is changing.
Sure, nothing is forever, however I think until the moment the paper money no longer exists, we also no longer exist, so the future of paper money with us no longer important, we also can not see it. At present, paper money is still very popular and convenient, I do not see any signs of decline, using paper money has become a habit, we are difficult to change this habit, want to change, we will need to go through the centuries and I do not think we can live to that moment