Bitcoin have the big chance to replace fiat. Becouse people in some countries were change their money in to bitcoin to save their wealth when their fiat price is fall against USD. Those country need to import logistic that they have to pay with USD. So I think people will prefer like to use bitcoin than fiat.
yes it can be there is always a chance but i think still it will take decades because still a very little number of people are using bitcoin and almost all the people also depend on fiat, therefore it is not so easy to replace fiat so soon.