I don't think NATO would have a choice, the leaders of France, USA or UK aren't going to be starting a direct war with Russia over these countries. I certainly wouldn't support a potential nuclear war in that basis and I don't think anyone else would.
This is kind of my point, why have a defensive alliance when the will really isn't there to properly enforce it.
Russia since the Soviet Union collapsed has posed zero threat to us militarily, apart from their nuclear weapons, they hardly even have a navy. The idea we need NATO that far East as some kind of bulwark against a potential Russian invasion just isn't right and creates more problems than it solves.