No bitcoin or crypto for that matter won't make fiat disappear, but it could be a good alternatives. Just look at how Venezuelan's adopt crypto because its fiat has been hyperinflated. Even Japan, who embraced bitcoin is not discounting their Yen. And as long as there are government and central banks, fiat will exist. There might be cashless society in the future but it doesn't mean that fiat will be totally eliminated and out of the picture.