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.
I dont think that it will last forever, but it wont be replaced soon. I know that technologies are too advanced and probably all members of this forum wants paper money to be replaced, but the entire world doesnt want that.
I wouldnt like to only pay with bitcoins, i really like having the paper money, and bills are pretty, i like holding them.
So i dont think that will happen, and if it happen, i dont think that it would be bitcoin, since there is not even 0.02% of the population that uses bitcoin.