The dollar is too big and its also way too overused to let the bitcoin take it over, the dollar will never be stopped!
This is really doubtful. That bitcoin will going to replace dollar soon. It is possible if government of US will take control of bitcoin.
But I think even them, they can't control this kind of decentralized crypto currency.
No one can control Bitcoin unless he/she buys the majority of bitcoin that ever existed. But I doubt that would happen because there are tons of whales out there that hold tons of bitcoins. And also, why the US government of all governments? I don't think the US government has any plans of controlling bitcoins because it doesn't make any major problems to them.