Currencies of individual states will exist until the need for them disappears. And this will be decided in all cases by the representative bodies of these states. The need for national money may disappear when uniting the economic and financial systems of different countries as it was done in the European Union. In all other cases, the currency of individual states will exist as long as the state exists.
In depends on how the state recognize a certain currency that circulates the entire nation. Somehow it cannot eliminate the usage of fiat money system, because it's very necessary specially it's a usual mode of payment used on both local and international transactions. Digital only exist with cryptocurrency patronizers but not the whole world.