It's hard to predict the future with certainty, but I don't think paper currency will be replaced Entirely by digital one anytime soon. While digital transactions are becoming more popular, there are still many people who prefer to use physical money for various reasons. Additionally, there are certain situations where paper currency is necessary, such as in areas without reliable internet or electricity.
We're already on a digital currency in my opinion. Our assets and liabilities are stored as digital data and most payment facilities are done purely digitally in most parts of the developed world.