What do you think if one day people do not want to use euro or dollar but want to use Bitcoin to buy goods? Bitcoin will rise in price, but will the euro or dollar fall?
The question for me is whether these fiat will actually be abandoned giving the fact that bitcoin is a digital currency which is not carried around like fiat.
I think even if it were possible that fiat is not used again, obviously the value will fall drastically because its exchange value has died and of no value. This is like trying to put a name in something that exist in vacuum.