Nothing good will come of this.
One of the repeated themes in Russian history is it doesn't matter how many soldiers are brought to the fight, it matters how many actually fight.
Best case scenario is that Russians don't actually want to die for this, and they will lose their will once Ukrainian anti-tank and anti-aircraft weapons start inflicting damage.
Worst case scenario is Russia achieves all their military objectives, and we sanction the ever loving crap out of them, but the Russians never leave and we and our allies never see any cause to ease up on the sanctions. That leaves us and our allies having to long term plan on not having any food, wood, steel, oil, natural gas, or coal from Russia, and that leaves Russia massively militarized but with deep economic wounds. That's basically the situation that Japan festered in for four years before they finally lashed out at Pearl Harbor. The worst case seems more likely than the best case, unfortunately. And the worst case will have ramifications for long beyond the time that the tanks stop rolling and the mortars stop launching.

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