Which Bitcoin to be hijacked by the government? All Bitcoin? Or all Bitcoin in a country?
If you mean all the Bitcoin in the world, it should be impossible. Remember that not all governments hate Bitcoin. Some countries even are friendly with Bitcoin as it has a contribution to improve the economic sector. They mustn't try to hijack Bitcoin because they know it will give a bad impact on Bitcoin.
Also, Bitcoin is a digital asset, it will be rather difficult to be hijacked by the government.