If we have Japan filling the Russian void after the Great War but not otherwise getting up to the idea of conquering China, perhaps with a stronger British and French presence and American influence, then one might see this divided China last. If we have a USSR then it will back the KMT and help subvert Manchuria as the USSR engages Japan, if the Russian Republic survives then it might also follow a similar revanche path, backing the KMT to distract Japan. The USA sought concessions in Manchuria as part of the Open Door that helped build the Japan versus USA mind set, so I think the USA backs a revanche China to some degree. The issue is just how broken is this China?
Can the KMT reassert central authority, break the warlords and move forward to modernize China, get industry and independence from the Europeans yet not run afoul of Japan to spark open warfare? It is this backdrop that a Japanese Manchuria must face. I think Imperial Japan can hold on to it within the stalemate of competing British, Russian and American interests, cross-cutting designs for China itself and a recognition that Japan is just another parasite feeding upon China. Long term it should be Russia, Soviet or not, that has to reassert itself in Manchuria, the support it gets might be none or all. If Soviet then you might indeed see a Communist insurrection and new puppet state like Mongolia, if a non-Soviet Russia it might get weird. I am doubtful the Russians care to back Mao and his brand of communism. Without WW2 you might see a longer lasting Imperial Japan stuck in the Asian version of a multilateral cold war, yet it may not be so clear cut who is on who's side. This is where I am ending up with an Imperial Germany, it backs China in an uneasy enemy of my enemy is my friend partnership with Russia to unseat Japan who is still British aligned but the USA is against both in China with France more an outsider to the evolving Chinese situation. Here I have ROC get further but holding less, as it gets towards parity with Imperial Japan the world moves closer to an Asian war. No one wants a revitalized China made whole but all sides play against each other with proxy China and its pieces, so more picking away at ROC through warlords and such. I am toying with a non-Soviet Russia just to warp things and a very chilly Anglo-American relationship to give Japan harder choices. With its empire intact, Imperial Japan can be a serious top-five contender even if it fails to see its economic miracle post-war as OTL, it certainly can get in the top-ten and be a very serious regional power against any one of the others. I painted myself into a 4 or 5 way superpower stand off. I do not know if it is a better history for China but it certainly is a different rocky road.