Yeah right government might choose their national currencies rather than bitcoin. Maybe if there was a new country and adopt bitcoin as a currency that could happen, but I think it is impossible. Fiat is not likely to be superseded by the bitcoin whenever I think. In the future will be developed into a bitcoin digital currency, not the fiat.
Bitcoin will be just an additional currency and the technology around will give difference in the usual fiat transfers.
Fiat will still dominates all money transactions in the world since it can support physical transactions unlike in bitcoin that only lives in digital world. But yes using bitcoin is really more less hassle when dealing on online transaction but not on physical transactions.
Yes, Bitcoin really help us in different matters but it doesn't mean that we forget the fiat currency, Fiat currency is more than important than all crypto currencies. Only a few countries who accept the bitcoin in government level, and a huge countries are not accept the bitcoin even i see many people don't know about bitcoin that it is a name of popular crypto currency.