That's a good point. We might end up in some kind of de facto stalemate because both sides have run down their supplies and new ones aren't coming in fast enough.
Considering the rate at which ammunition is consumed, and the cost of manufacturing it, that's the most likely scenario. From what I understand, neither NATO nor Russia could maintain operations for more than a few weeks before they're scraping the bottom of the barrel.
Also, this is rapidly turning into a Russia wank. Russia manages to strike Alaska with impunity, and no one thinks to reinforce in until it's too late? The Marines invade Sakhalin but then the Joint Chiefs say "Eh, fuck it" and leave them hanging with little support? I mean, this is the US we're talking about. Even with a land war raging in Eastern Europe there's still plenty of air and naval assets to support a massive ground operation into Sakhalin, they wouldn't just throw the Marines onto the beach and say "good luck boys!".
If this happens, I'm un-subbing. This TL has been a very good read so far, with a few unlikely events occurring, but so far has stayed out of implausible territory and I hope that it stays that way.
This TL is very readable, but started at implausible and is rapidly encroaching on Modern Warfare 3 territory.