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.
More like fiat is used cuz they are here from start used in the world. Money it self is something that we all used to have one way or another so with digital currency we have some new option on this and hopefully we will be able to used every day in some time.