Future remains intact of the paper money as worldwide there cannot be one currency. Paper money will not disappear anytime soon, maybe it will be replaced by something else similar to paper. Bitcoin could act as an secondary currency if country adopts it.
Paper money would not disappear since its been used for many centuries even there are lots of kinds of currency out there, one would be replace and one currency would exist . You stated that bitcoin would act as secondary, yes it would since theres no possibility that bitcoin could replace paper money since btc was made of codes it a different story and shouldnt be compare.
In the future it could be more on digital money rather than paper money but we cannot predict when it will happen. There is a good possibility that it will happen because the world is starting to switch into paperless economy.