NATO might not get involved, but NATO expanding membership is a reality that Russia will have to deal with (e.g. Finland). One of Russia's goals is (and has always been) to create a buffer of neutral or puppet states. Russia wants Ukraine to either be like Belarus, or shrink to accommodate annexation for supposed "independent republics" (and Luhansk and Donetsk are just the tip of the iceberg).
The smaller Ukraine gets, the more likely they are to join NATO. And then Russia will have no choice but to have NATO on its doorstep.
Even if Russia "wins" this war with Ukraine, they may have cut off their nose to spite their face.
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