I agree. I will point out that some of the other balkan countries will break for Russia or be embroiled in war. Example: Serbia! The question of Russian allying versus European Intergration is a difficult one in many places.
But what is the context though? If it's something personal, the US might now want to Intervene. If, in the otherhand, the Chinese feel the can tip the scales, they may be tempted to ally with Russia.
The questions would be exactly to what extent the russians will eventually advance, and how long and how effectively they will be able to hold on. I doubt not too long, but war does help economies.I think that, assuming the russians begin their advance, and that the US has up to this point not intervened, they will be able to push at least to France. as soon as the russians begin their advance, of course, the US will be all over that. But that takes time, and the US doesn't have the military prescense in the region it once had. if the Russians push so far back as to essentially claim the continent, There will be a more intersting question regarding whether they can sustain themselves. If they don't push even as far as france, the question is moot.
If the russians can't capture land before the trenches are in the ground and the front lines are drawn quite clearly, they're screwed. There advantage of military might is all they have, once the advance has slowed, they'll need to go SUPER-WARTIME ECONOMY MODE to even have a shot of keeping any of that territory. if they somehow manage to hold on for a year and have begun gaining the fruits of the European Economy, WW3 will start. The US will press China into making a descision, and as I said, if it looks like the russians have a good chance, they may well jump ship.