I think Europe would then be forced to intensify its relations with China. Since China has so far been somewhat cautiously supportive of Russia’s military expansion policy, or at least has not decisively sanctioned it, I think that would be a reasonable way of minimizing the risk of military aggression from Russia in the first place. I hardly believe that Russia would risk a military conflict with Europe if they could not expect support or even just tolerance of such actions from China. The consequence for the USA would then not only be a loss of strategic military influence in Europe, but probably also considerable losses in terms of trade and so on.