As I understand from this kind of things nothing can happen to bitcoin and to blockchain if this story happen. If attacked the 51% (or even more) of the blockchain can be a big damage but the rest of network can continue its work and the part our of work can (will) be replaced with other mining farms or source of mining. This is the superiority of being decentralized. Every cell can act independently from the other ones. Maybe I'm wrong (I repeat that I am not a good specialist in this field) but the meaning of decentralization (as a term) is exactly this. Every part of the entire is independent from the entire. The overall system can be damaged if damaged part of it but never die. The remaining sane part act as an entire even without the damaged part continuing in this way the normal activity.
If the 51 attack was ever to happen, it probably won't kill Bitcoin (maybe in the long-term it would even strengthen it, who knows) but it would cause a massive damage.
I'm not sure whether there are tools to blacklist misbehaving miners, so the 49% could take over. But my point is, the distribution-by-country does make some difference from security point of view.
I haven't told that the distribution by country is a good thing or even an indifferent thing. All my post speak about the situation after a probable damage. So have in mind exactly the damage caused by such situation in which the Chinese market dominate the production of bitcoin. Otherwise have no meaning to do such reasoning like I did in my post. I accept that this kind of distribution of "power" over bitcoin is a possible risk. And it would be always. But my point is that even with probable damage the network must survive. Will suffer (in the meaning will be restricted) but will survive and will act as an entire full entity even after this possible damage. That's the power of being decentralized of bitcoin. Cannot be dominated because has hundred "heads" and hounded "hearts". If one of some of those can be dead the other ones can assure the normal life of it.