I’d like to think that if it was from NK, it would likely be MAD of NK, but not all of Asia. If China was attacked for instance, they have the capabilities to

I’d like to think that if it was from NK, it would likely be MAD of NK, but not all of Asia. If China was attacked for instance, they have the capabilities to ensure MAD of any other nation or all of them, via a network of nuclear armed submarines - from undetectable locations - even after the nuclear destruction of their mainland. This makes it pretty unlikely for another nation to fire nuclear weapons into China.