Are you sure? Even government create their own digital currency, it will not guaranty that it will replace the fiat money. Fiat monetary system is exist long time ago and I think it will continue to exist whether there is a digital currency because digital currency is just an alternative to fiat. Many people still doesn't know how to use digital currency and government also doesn't want to accept and legalize digital currency specially bitcoin because of decentralization.
Digital currency should not serve as an alternative to fiat currency at all, and in the case of issuance by the central bank of the state, the digital currency simply becomes a form of fiat currency. States can experiment as much as they want with concrete and other similar alternative currencies, but the main bet will always be on their own digital currency.