Paper money will stay forever.
Why? Because its easier to make than coins.
Paper money is still there because bitcoin is made due to the needs in the digital world. Many of us is thinking what comes tomorrow because they are afraid that everything will be replaced by technology. However I'm still believe that paper money will last forever.
Paper money is going to last for a long of time but it is not going to last forever, if technological progress keeps going forward then it could be possible that technology like the one we have now is available no matter your level of income and that will bring the demise of paper money in the future.