It would be very impossible since I don't think the government would want to lose control on their citizens. Bitcoin can be easily hacked. The government could possibly lose alot of money if they get hacked. But it could happen if the current government of every country is squashed.
The advanced technology is very successful. Anything can happen in the future. So it may be possible that governments make some regulations through which they will be able to handle bitcoin and will be able to maintain the affairs of the state with the bitcoin currency so it is possible that bitcoin will replace dollar soon.
if dollar completely replaced by bitcoin i think the same thing could happened to human too ,
i mean just like the sci-fi movies where the story telling us that human will get replaced by machine ,
it's sounds like so scary and i don't want to see it happened ,
better to go for both bitcoin and dollar.