As long as physical currency can still be used by people for buying, selling , holding etc. If only digital currencies controlled by centralized financial institutions are allowed, you will likely lose full control over your funds unless you use a decentralized currency system that gives you full power/control over your funds. And probably use some sort of decentralized Banks that let you plug your node/wallet to their wallets/nodes to benefit from better services like better interface, additional security, smartcontract services etc.
This is my biggest fear as well. What if the government just decides to implement a new wealth tax, that takes away 1% of all your investment and savings. If we don't have any cash anymore then there is no way we can get around such things. The government will have full access to our funds whenever they want. I am really scared because this could lead to miss use of our money by the government. Also if money is only available digitally then the government could block the transfer of any funds abroad.