You can imagine how huge the panic selling of Bitcoin would be by then, and it will get to the level that you will not be able to sell your Bitcoins again because no one will be willing to buy it from you. It is not until this time that you can say "the government has attacked Bitcoin." Restricting, banning and finding ways to regular Bitcoin transactions for the sanity of the world is not an attack, only that you guys are not appreciative of what the government is doing, particularly for not clamping down on Bitcoin.
The story is different if we talk about one government or all the governments of the countries combined, because 1 or 2 governments will never be able to stop or destroy bitcoin because bitcoin is decentralized. If a country bans or seeks to eliminate bitcoin, miners will move to another country, like the Chinese government did with bitcoin, but things will become serious if governments join forces and attack bitcoin then surely bitcoin will be difficult to survive.