I believe that an arrangement could have been made so Japanese returned to the borders from 1937, while Chinese really wanted to take care of Mao and the Communists. The details may vary and include a port or two being ceded to Japan.
The biggest obstacle is getting Japan to agree, China would probably slide in as it was (at least in the short term) weaker party in the conflict. Chiang realized he was sapping his strength and the longer he fought the Japanese the weaker he would be for an eventual showdown with Mao. Had the Japanese been able to approach the negotiation with goodwill and willingness to openly negotiate and had IJA been curbed in 1936, after 2-2-6 incident took place, the Pacific War as we know it might not have been.
As for Europe, well, obviously British would have a much easier time fighting Rommel in 1942. Even more US troops, airplanes and navy would be present in ETO and perhaps USMC would take part in an invasion (I wouldn't mind seeing this in a timeline, BTW).
After the war, China would probably still end up Communist, Chiang was way too corrupt to survive for long. Japan would have (probably) its Algiers/Indochina moment in Korea and Manchuria and Taiwan might have remained Japanese to this day, accepting the Chinese refugees as mainland fell under Communist rule.