While I don't believe it will completely replace paper money, I believe an equilibrium will be reached in which both are used in their own context. I think of it as the co-existence of paper mail and e-mail in our day. The equilibrium is determined by their intrinsic advantages: having something physical vs. speed and ease, and it is now shifting in favour of the usage of e-mail because of environmental considerations in the billing of companies. In the case of bitcoin vs cash, the location of the equilibrium will depend much on the government policies, especially on taxation; which is for the moment an unknown.