Like joering, you have failed to specify how the government will magically kill bitcoin.

Spend enough money on machines to have 51% of the processing power and subvert the integrity of the keychain, thereby making the entire system untrustworthy.

I cargo-culted that explanation, but it sounds good to me.

also, they can simply legislate to ban it, for whatever reason the want like someone mentioned before. Its up to you whether you want to break the law or not, but most people will not.