In my opinion. until any time the fiat currency will be needed and used throughout the world. technological advances in the financial sector will not affect the existence of fiat currencies. Digital currency is used to facilitate everyone in choosing transaction tools so that our work will be easier. and fiat currency is used for people who do not have a digital currency.
I think the answer is to ask yourself, are you still using fiat to buy something? I think most or even all bitcoin users must still rely on fiat to pay for their daily needs, you are right that technological developments will not change anything on fiat as the main currency
But if all of the facilities will be available with the payment of cryptocurrencies then these users of cryptocurrencies will start to use their own coins. Right now people are using fiat because they are finding hurdles in using cryptocurrencies.