This sounds logical,but it's just too must theorizing and fantasizing,if you ask me.
The government could destroy the blockchain,at least inside the borders of it's national teritorry,if it wants to,but what's the point?Where is the benefit for going such thing?If China was a normal country,the citizens could probably sue the government for destroying their crypto wealth,by conducting 51% attack and ruining the value of Bitcoin.This is all just a possibility.
I never said any country could destroy Bitcoin. The topic is not anything about any country destroying Bitcoin but merely just them restricting the use of it like how China does with the GFW. It's completely feasible and arguably even easier than trying to ban VPNs and Tor.
I doubt China could destroy Bitcoin if it wants to. Consolidating that much miners is not possible within a reasonable timeframe and without the news of that leaking.