What are the basic things that make you think like that now?
Do you know the number of people living in this world who still use paper money every day? And one more thing, you also need to know how much supply of Bitcoin has been circulating and has not been circulating in the market for now. Because if you think that Bitcoin will be enough to be used by all people in this world, I think there is something wrong with your thinking.

Why, because Bitcoin can still be used as the main source of payment without having to eliminate paper money from this world, besides that paper money that is still used by all humans today can be a payment option when someone doesn't have Bitcoin or other digital currency in themselves. So there is no need to eliminate paper money even though there are better payment solutions available for everyone to use.