Don't get too carried away, wouldashouldacoulda.
At that time, Stalin would've had to have backed Mao completely. He didn't want Imperial Japan approaching his border in the first place, he certainly wouldn't mind throwing more bodies to keep a nuclear USA of the continent.
The "greatest generation" was tired of that war, and wasn't going to have it all out with Uncle Joe.
And in the end, then what? Perhaps if we had unified Korea at that time, they would have had 50 years to becomes a socialist "ally" the likes, of, say...France?
Who are the only friends we have in Europe? The East Bloc that we also didn't let Patton free.
If Truman hadn't "lost" china in the first place the discussion would be academic.