Thinking on it, the Nationalist war effort in China really came apart in the Manchurian Offensive where a whole army of his surrenders thus negating his ability to keep a lid on the Communists. Mao's policy was more then happy to give territory to the Nationalists in order to destroy them from within, but what if the Communist forces are given space and 'contained'?
Instead of commiting to the ill-fated Campaign for Manchuria, Chiang withdraws his forces from Manchuria and focuses instead on strangling Communist forces in the Yellow River area and in Yenan, using geography and superior artillery and air power to force Communist armies in China apart and eventually crumble.
Even though, such a endeavour would be a near thing in itself, only kept together by Chiang's own ruthlessness and ability to keep the Communists from really solidifying within his territory. Therefore a invasion of Manchuria itself would not really be possible without untieing his efforts int he rest of China. Eventually the US and USSR step in and demand a parition of China much along the lines of Korea and Vietnam.