chances are very small. fiat has advantages in terms of direct payments and real value. digital currency will be useless when there is no internet reach. it is certainly very detrimental. so, the existence of fiat is still very bleached.
Although the chances are very rare that bitcoin will replace fiat, but i think that with increasing demand of bitcoin is in fact making bitcoin more stronger. i think that in such modern time it is very difficult to think about the world without internet, because internet is not only use for bitcoin for a number of other purposes. so we cannot spend a single day without internet. I think that its difficult that bitcoin will replace fiat but will surely reduce the use of fiat currency.