At present, it is impossible for digital currency to completely replace paper currency. With the development of society, the progress of science and technology, and the reproduction of human beings, people will finally realize the advantages of digital currency and use digital currency more than paper currency.
Unless we create an infinite, indestructible, efficient and eco-friendly electical source all over the world, we can't fully adopt digital currency because if we start too early with some countries not having that kind of electricity source, someone malicious can commit financial terrorism by shutting the power grid that causes blackout and it only takes about 1 or 3 days in my opinion to make a country collapse with a crippled economic circulation not to mention some real deaths caused by the blackouts. I think for now, we should focus on making a coexistence rather than taking over because we still haven't solved the energy in the equation to fully take over the old ways in money.