Does anything about Mao's OTL rule suggests to you that he had any sense?
This is the fascinating thing about Mao; he did so many things that amounted to shooting himself in the foot but ultimately helped him because they killed off his rivals, both real and potential. He did things that resulted in utter national disasters, but he wasn't concerned with the strength of the country so much as the strength of himself. This man was an opportunist to the extreme of extremes.
With Mao Zedong, it seems that without serious foreign intervention he would not be content of anything short of being the supreme ruler of China, a position that would require there not being any other Chinas (i.e. the RoC) in existence. This line of thinking was part of the reason why Mao cared more about defeating the KMT rather than fighting the Japanese, who, before 1941, he hoped would make a deal with Stalin to split China into a Communist north and a Japanese-occupied south.
Thus, as long as the KMT continued to exist on mainland China, Mao would've been finding ways to subvert and eventually destroy it. He may have made some peace or cease-fires in the short term but ultimately there would have been war in which one side would have to lose totally or be reduced to a marginal territory like Taiwan, Xinjiang, or Manchuria.
It is thus necessary, in order to cause a stable north-south Chinese split, to kill Mao, but not too early that the CCP can be crushed by the KMT. Therefore, I point to the time at Yan'an, during which Mao was pissing off the Russians (and indeed Stalin himself) by defying Moscow's order to resist the Japanese. This would be a good time for Stalin to look at one of Mao's impertinent, lie-filled reports the wrong way, reach for his telephone, and order the Chairman to be disappeared (along with Kang Sheng) and replaced by someone more loyal. Maybe someone like Wang Ming.
This replacement of Mao would make the CCP somewhat less diabolical and also less successful in the long term, and thus could very well yield the required north-south China split after Japan is defeated. If the CCP spent few years actually fighting the Japanese, they could strengthen their base in the north and with Soviet supplies and backup, fend off Jiang Jieshi's attacks. Eventually there would be a cease-fire and negotiations would result in a split China.