I do not believe fiat can ever be replaced as the government exist.
The government could ban bitcoin so the value of bitcoin could drop to non existent to one's country
I am Sorry but I dissagree with you, there is fiat of some country that being worthless then the people try to buy bitcoin to safe their wealth. I think there is still a chance for bitcoin to replace fiat.
Haha. You need to know that Governments will try their best to stop this from happening. No government wants their people to use other currency except their national currency. Therefore, there is no chance for bitcoin to replace fiat unless the governments collapse