Barbarossa is delayed to 1942 and as a result the Soviets are able to handily beat it off before going over to the offensive. This means Chiang is never able to convince Roosevelt to convince Stalin, in his moment of distracted desperation, to give up Soviet de-facto control over it. Hence, it ultimately winds up as another Mongolia.
The tough part here is how to avoid the Soviets handing over the region if/when Mao comes to power. Butterfly away CPC victory in the Civil War perhaps?