Without Mao, the situation could turn like the Spanish Civil War, where the Soviets turn their back on the differently aligned communists. If the Chinese Communists don't align with the Soviets, it hurts their chances of support when the Soviets finally shake off the Nationalists. If the Communists are in open defiance of Moscow because of the lack of Stalinist Mao, then the Nationalists keep the support of the Soviet Union.
Ultimately, it might turn out better for the Soviets in the end. I don't think it really affects the Japanese invasion. The Chinese can still shake them off, but how strong the Communists are after it will be important. If they become a force on par with the Nationalists, then I could see the Soviets mediating a peace between the groups. A fractured China, Manchuria staying under the Soviet fold, with the addition of Xinjiang. A bigger headache for the US, as it will complicate Asia more so for them. The Soviet Union won't have to worry about a Chinese threat since an independent Chinese Communist state would occupy the area south of Mongolia and largely rural. Basically, the majority of whatever Chinese states result from this are going to need Soviet backing, or are going to seek it.
Damn, that was a lot of Communists, Soviets, and Chinese.