If Ukraine falls, the plan B is securing the land connection between Poland and the Baltics from a potential offensive coming from Belarus, and cutting Kaliningrad from Russia-Belarus. Conversely, Russia’s plan is establishing a land connection to Kaliningrad and cutting the Baltics, although now that Finland has joined NATO, it isn’t that much of an useful goal for them anymore.
All in all, a direct Russia-NATO war is extremely unlikely, unless there are extreme geopolitical realignments in the EU.