I think if the digital currency were become famous in the world, maybe paper money were dissolve and become part of the history of different nation. Also, it okay to more users the digital currency, because it was easy to use but it hard to protect due to a lot of hacker.
Probably in some advanced and well off nations this could be possible to go mainly digital but I think paper money would still be relevant even if that happens. Even now we can observe that a lot of countries are venturing more on the digital side but the challenges of going full digital is heavy even on these countries. So paper money im sure will be around for a long time still