Russia is hardly going to "attack Europe" en masse; it's all about salami tactics. They'll gear up and, say, shore up their areas in Ukraine, or fully reinstall Assad but as a Russian puppet. Big, but not big enough to draw Western forces in properly. Could Russia try a mass invasion of Europe? Possibly, but they'd bleed like anything doing so, not least because the US, for all that it's not what it was in superpower terms, still has frankly absurd levels of firepower stationed in all sorts of convenient locations around the continent. I think Russia's ambitions will be fairly calmly paced to ensure that whatever they do it'll never seem quite big enough to draw Britain/France/America into a full on conflict.