One version of the decision for the Greek war is that Mussolini feared it would coalesce opposition & he rushed the attack in order to preempt any organized opposition. I have no idea how accurate or important it, but it does suggest to me a route where there is no Italian/Greek war. Instead the war with Britain is confined to Africa and the sea. In that case the German decision might lean further towards no assistance & a eventual Italian/Brit armistice. Particularly if it is clear the Red Army has not collapsed. It seems this would be easier were the Balkan nations lately unoccupied by the Axis armies.