I don't think a successful 51% attack would kill Bitcoin at this point nor do I think anyone capable would be willing to attempt it. It would take a great deal of equipment and money to pull off such a thing. I do like the idea of governments with massive amounts of hashrate closely monitoring chains for any sort of forking while they wait for a massive transaction to receive confirmations. Makes me think of the new Loki show and divergent timelines being managed by the timekeepers...
And if a government tried to attack Bitcoin, wouldn't it be extremely likely that they will be exposed? How could you pull off such a massive operation, whether it be hardware orders or electricity going through the roof at a specific geolocation, or anyone else involved in the operation saying a single word, the government/actor trying it would almost certainly be exposed.
Is there any way to roughly identify the geolocation of the hashrate production through means other than whistleblowing or obvious behavior like huge hardware orders?