The elephant in the room here is the Schlieffen Plan. That would pretty much ensure Britain enters the war regardless of any official alliance with France or Imperial Russia, and since the Germans never had any effective means to defeat the British they were guaranteed for an exhaustion war that was not within their power to win.

The bigger problem with the Russian Revolution also was not the Germans but the Ottomans deciding to enter the war and cutting off the Russians from arms imports and food exports. That did more to create the Soviet Union than any German battlefield victory did.