If Mao was defeated, it would likely have happened while Stalin was still in power.
I suspect that Stalin would then proceed to fund communists in China. There's nothing the Chinese van do to stop it. Their border with the USSR, is too large.
I dont think he would invade. That essentially guarantees WW3, and he would be fighting it, alone, while is country is still devastated by WW2.
Communist China is fairly capable of forcing communism with a supportive USSR.
Koumontang China would never be able to pull that off.
The China USSR border becomes even more of a flash point than it was IOTL.
Constant border skirmishes, or WW1 styles trench borders stretch its span.
China would not be Japan, or Korea, but it would not be India either.
India has a large communist party, no border with the USSR, and an enemy that has border friction with the OITL communists.
China, in this scenario, would at the least disappear anyone in a communist party. The communists nearly beat them in a civil war, and I dont believe the strife would fully end.
There's a decent chance that the US will actively work to help industrialize and empower China, to hurt the USSR by proxy.
The Korean war, never happens here.
The war in Vietnam is much harder on the North without easy access to supplies.
Japan, is less important to American eyes.
There's no telling precisely what the USSR would do about this. It might put them enough on edge to do something stupid.
Domino theory, in this scenario, isnt a thing for the US, but in the same way, the USSR, isnt expanding their buffer, they are instead, being surrounded.