You're forgetting the US military here, while it would take a bit to mobilize ground troops, you've seen how fast we mobilize the airforce. So, Russia would really only have until we get things rolling.
I could see NK using the distraction to attack SK or something though.
And yeah, this is deep into Armchair General General territory.
Well, I suppose if Russia's committing national suicide in this hypothetical, the DPRK can't allow themselves to be out-crazied.
Just as a heads-up, though, the DPRK are actually outnumbered by the ROK nowadays, and they're much more focused on the static defense due to their strategic priorities. In a one on one fight, the ROK wins, though Seoul also loses.
But now, we're talking about a hypothetical in which the Russians are pulling out WW2 tanks (that is, not even T-55s, which are still on reserve status, but stuff like the IS-series and the T-34) out of storage (where? I don't even think the Russian government maintains official stores) and putting them on a modern battlefield in the hands of people who have never trained on anything older than the T-55, where the regular army is being held back and reservists are being used as the main thrust of the invasion, where logistics are completely irrelevant (because of said regular army protecting the ever-loving daylights out of them), where the French and Germans are both actively refusing to fight because
reasons, all to facilitate an outcome where the Russians will be in Spain before America gets its boots on. I...I'm not going to say what I think, except that I think we've left even Armchair General Station in the dust. I'm just going to step out now.