well its depends where do you live.if your country govt support bitcoin then it will replace fiat currency in few yrs,and if they dont support then forget it.simple

your response is quite funny. I think Op is asking the question based on the whole countries of the world and not a particular country, your country or mine.
And my response to the asked question is that bitcoin is not yet in that level and for the "ever", I think no is the answer because it will still remain bitcoin as digital currency.