There may be governments that will be threatened by BTC in the future and they may want to control or destroy bitcoin. However no one has shown me how they could do it. That is the power of open-source distributed computing. There is no point to attack. My computer could be attacked and taken offline, but there are tens of thousands of such computers across the world. Going after them would cost many millions of dollars and would likely have a tiny effect. It's just not logical for governments to act in this way.
All they gotta do is strangle the on and off ramps for fiat. That could be implemented tomorrow with very little expense.
There will always be a hard core of users and loops will gradually close, but it will always need to interact with fiat in some way for many.
It wouldn't be end of it, but it would suddenly become a lot less useful to the majority.