The best case scenario of a brief spat followed quickly by the DPRK regime being overthrown and a South Korean-led reunification, would leave China with a country with strong ties with the US on it's borders, which neither China or Russia would be happy with.
I'm not sure about China, but Russia, IMO, would be happy to have a land border with the Republic of Korea. It's a way better trade partner than DPRK. Regarding the "strong ties with US" and possible US troops near the border, Russia already has plenty of NATO troops on its western borders so there isn't much to lose. And apparently it won't be worth joining a war.
But, unfortunately, the South Korean-led reunification you're talking about is a VERY unlikely scenario. For 60+ years, there are two different nations formed already. They've passed the point of no return on the question of reunification long time ago. By the time of reunification of Germany, the gap between the economies of FRG and GDR was about 5 times (if I remember it right) and it still leaves a mark on the present-day Germany. The western Germans still pay the "solidarity tax". Now back to Koreas - the North Korea is over 20 times poorer than the South. Even if they hypothetically reuinite, this will put a HUGE stress on the economy of RK. I doubt they would like such "happiness".
And to think that NK's own people was used to test the poison in that formula.
Well it wasn't North Korea that first tested VX.
It was first sythesized in the UK in 1950's and was supposed to be a pesticide, but it turned out extremely toxic so it was banned from agricultural use (300 times more toxic than phosgene used during the World War I).
Currently, VX is officially adopted by US and Russia only, but may also be possessed somewhere else (including North Korea). It is said that Saddam Hussein had used VX against Kurds in the '80s.
Well, it has 0-Ethyl Methylphosphonothioate, although I guess that's not quite normal
It rolls right off the tongue.
Well, I'm a chemist, so such names are fine for my tongue.
Chemical weapons isn't my speciality though (neither the organophosphates), but we've learned about them in my university.
Currently, I'm working on some compounds that are supposed to be UV absorbers, but... who knows
Reminded that this is the same poison used in Syrian Civil War.
No, it's a different one. The one reportedly used in Syria was sarin, which is a nerve gas and an organophosphorus compound, too, but an older one (discovered before WWII by Nazi German scientists who tried to make a more powerful pesticide, too).