Not only the introduction of blockchain technology, but also the partial use of cryptocurrency for government purposes is quite possible, especially if the government follows the trends of world leaders. But I'm sure that no government wants to lose its monopoly to completely replace national currencies with cryptocurrencies.
Agree, Government will keep their fiat cash and always keep it. Because we all know crypto currency cannot be controlled. I think government will create own crypto for their national currency at the future.
States have already started issuing their own cryptocurrency based on their national currency, these are their digitalized central bank currencies, that is, their stablecoins. It is they, and not bitcoin or another decentralized cryptocurrency, who will partially displace paper money from circulation. Bitcoin cannot be related to this process, since by its nature it is not capable of it.
New types of digital money should not lead to the complete disappearance of paper money. All their types have the right to exist, they must complement each other with their special properties.