Well, it's all a bit vague of course, given our premise is ill worked out. Who says France isn't gonna leave Germany hanging when they've finished creating a perfect storm (of the German armies rapidly surging east to prevent a possible Russian intervention while Britain is blockading its coast), or even stab them in the backs?If the prospect is going against France and Germany combined, then the prize is not worth it. So many relations existed between different rulers of so many different crowns that, if what you assume is true, would mean that no wars should have been possible.
It is far easier to act as a host for his nephew than fight a war in which France and Germany fight together (a combination which Russia + Britain cannot beat).
Presumably something in the lead-up causes that certainty for Germany, but that same something likely determines where A-H and Italy end up.
Russia vs Germany with half-hearted French support for Germany is still not likely to be a Russian victory, but Germany doesn't know that - so why would Germany even create a situation where it risks that fight (and especially, risks having to fight while France rolls over Wallonia-Belgium-Brabant and then stares at Britain across the channel, while Germany's stuck with a Holland-with-Brits-in-it AND a wide open front with Russia)?