Okay, switching gears a bit, what about no Northern Expedition (for whatever reason)? Could you end up with a more or less stable partition of China into a Nationalist south, a Beijing 'national' government, a Communist republic in and around Jiangxi (or further northwest), and Manchuria either under the Zhang 'dynasty'? Independent warlords are eventually defeated or absorbed, but none of the four Chinas is strong enough to conquer the others and unify the country. Perhaps because each one has a foreign backer - the British and French in the south, the Germans in Beijing, the Soviets in Jiangxi and the Japanese in Manchuria?