Who would you expect to fight and who would you expect to make excuses?
If you've read the CIA document linked above, the Soviets figured that entire countries would surrender to them. I don't think it's (all) that easy, especially since Russia's aggression has considerably increased the readiness of Europeans to fight for their countries (even in sluggish Germany, the ratio went from 22% to 61%, for example).
The Eastern Europeans and Scandinavians, most wary of Russia due to proximity, would certainly fight, the fate of Ukraine present in their minds. I'd figure the West Europeans and North Americans would join the fight, but perhaps be less enthusiastic about it.
Hungary, Slovakia, Bulgaria, Turkey, Portugal and Spain are the candidates which I'd deem unreliable. Hungary and Slovakia have pro-Russian governments; Bulgaria is the most pro-Russian country in Europe; and Portugal and Spain won't feel as affected due to the distance between them and the threat. Spain is also ruled by a fiercely pacifist socialist government.
Turkey is a wild card. Erdogan wants his country to become a major player in its own right, he'll do whatever he thinks helps that plan the most. In the past, he's been as likely to work against Moscow as for it.
At the end of the day, NATO's reaction would also depend on the nature of Russia's aggression. If they're stupid enough to support their hypothetical incursion with activities in other NATO states, they would certainly elicit a stronger popular response.
And they're probably stupid enough to do that, too. Just look at what they're doing now—airspace violations, explicit verbal threats, acts of sabotage, even targeted killings. If they were smart, they'd stop making Europeans feel threatened by Russia.
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