Nope. I very doubt government will want to relinquish control...
As a sub currency it could gain mainstream use but i think there will be much blood before BTC replace the Dollar.
I dont think so, I mean never dollar was set to be a fiat used in every country for essential transactions and tradings for the past century and I think it will not be implemented worldwide due to the fact the bitcoin is just making it name and it will run many more years to be officially established in different countries worldwide and becor it may happen someone must fund a free and international wifi for transactions.