Actually China already banned bitcoin, so yeah. but I think any country couldn't do anything about controlling them, because bitcoin is decentralized, and correct me if I'm wrong but, I think no organization or company has control over them.
If bitcoin is illegal, why it is now existing and accepted by the other countries? It will not be banned because bitcoin is legal. Actually, it will help to grow the economy of a country. There will be no reason to ban bitcoins in any government because their country will benefit from it.