Before he became General Secretary, but while Stalin was a high government official, the US, Britain, France and Japan literally invaded Russia:
https://en.wikipedia.org/wiki/Allied_intervention_in_the_Rus...
The operation against Maduro was launched from countries in the region aligned with the US.
You also rule out the possibility of an invasion of Seoul, as though it would be "unfair" -- when you're advocating for and actively in the process of tearing whatever remains of the concept of international law to shreds, what makes you think PRC would be inclined to play nice?
I don't see what's unlikely about this, it's basically NK's defense strategy.
It wasn't just carriers in Maduro's case. The operation was carried from multiple places, including out of Caribbean countries aligned with the US. The US was literally signing deals with those countries months in advance.
Who would those countries be in an hypothetical NK strike? Because those countries would suffer retaliation.
China's primary concern is resource extraction from Venezuela, which is why Trump immediately clarified that they'd make sure China still got their oil deliveries.
Russia is stretched way too thin right now to do anything meaningful about it.
Venezuela was basically being run by Cuba. Maduro was really only a figurehead. The military and government was functionally run by imported Cubans which is why a coup wasn't possible.