"External Threats" and "National Security" are reasons why hardliners get into power...
As someone who was fortunate enough to leave the regime, if that insane "nuking China" thing happened, PRC would never have opened the borders (or if it ever did, it'd be very controlled and not as open as current timeline) and it'd be another North Korea situation (but more massive) and mass poverty and mass starvations well into the 21st century.
This timeline, Chinese people can actually leave. I mean my family is one of the many that left.
So... If that nuking happened, then do you think PRC would still allow people to leave in that timeline?
That timeline would have a lot of Anti-Chinese sentinment (as in hatred of Chinese People, not just the government)
There's no chance I can even get in the US, I mean just look at how the west closed borders to Russians... so now Russian dissidents have a hard time trying to escape.
I mean perhaps it'd satisfy a lot of US White nationalists, but there'd be a Billion people suffering... that's not good...
But disclaimer: I'm Chinese American so perhaps I'm biased and have sympathy for people in China that have nothing to do with the CCP.