I have been reading Guderian's (and von Manstein's) memoirs lately, and one particular incident the former relates about the invasion of France stood out. Apparently, just after crossing through the Ardennes, but before capturing Sedan and crossing the Meuse, Guderian was forced to visit von Kleist's HQ for orders. To do so, he was flown in a Fiestler Storch. On returning to his corps HQ, the pilot evidently was unfamiliar with the terrain, and inadvertanly flew the plane--which was slow and unarmed--over French lines. IOTL, Guderian realized the mistake and managed to get the pilot to get to his HQ before fuel ran out or they were noticed.
WI, instead, they were forced to land behind enemy lines, or were shot down, and Guderian was captured or killed? While XIX Corp's staff attempted to discover what had happened to him, they would of necessity be distracted from actually leading the Corps. Furthermore, any replacement leader might not be as bold (or so willing to skirt the orders of his commanders. So the breakthrough at Sedan and the race to the Channel Coast, consequently cutting off Anglo-French forces in Belgium, might not even happen. The Anglo-French forces might be able to either defeat the attempted breakthrough and force the Germans back to their starting lines, or retreat in good order behind the Somme. With additional forces, the second phase of the Battle of France might not occur, trapping Germany in a prolonged attritional campaign similar to the First World War. Under this situation, I suspect Mussolini would not attack France, and Germany would be defeated much earlier than IOTL. However, this would probably be a negotiated peace, not the unconditional surrender of OTL.