Since we're right in the midst of Stalin's death, it's very important when the war ends. If the end of the war is a successful UN offensive in 1950, Stalin's still alive when it's all over. Since that's the simplest scenario, let's explore that one.
First off, if it's over that quickly it's probably seen as another chapter in the "setting of the board" as it were, rather than the first major test of the limited war doctrine. Any loss of prestige Stalin does experience really won't affect his lock on power.
Similarly, China's lack of intervention wouldn't signal weakness so much as a continuation of the status quo. China won't have arrived on the scene as a regional power, it will have continued to be what it was before: a nascent power, soon to take its place.
An earlier Sino-Soviet split does seem possible. Considering Stalin wanted the Korean War to make up for the lost treaty ports he just gave up to China, he'd be pretty pissed if they lost the war and China didn't even bother to intervene. But what would he be willing to do to China? What could he do? What did he do to Tito? That's what he does to China, right?
Speaking of, a more proactive Chinese participation in the Non-Aligned Movement is another likely possibility. And if China does join the NAM, their support for the Viet Minh is probably affected. In the most extreme scenario you could have a proxy Sino-Soviet war where different factions in North Vietnam fight each other. Less extreme, you might find one side purging the other, or at minimum a factional cabal of rulers paying heed to different masters.
With a lot of luck, the US can find a better horse to back than Diem. With like ALL of the luck, in a world where the Soviets are mad at China, have lost in Korea, and thus decide they're just totally over Asia, you can peacefully reuinify the country. But considering how poorly the US understood Vietnam IOTL, there are plenty of paths where the war rages as per OTL as long as China or Russia are still lending a hand.
One possible consequence of a loss in Greece followed by a loss in Korea is that perhaps Soviet power projection looks weaker to other potential rulers, particularly in Africa and the Middle East. But the reasons these rulers had IOTL for joining the Soviets still exist ITTL. Who would change their minds? But we're still pretty far off from most of those interventions anyway. The most immediate are Egypt and Syria, who were PRETTY motivated to find any kind of help and would probably have allied with Monaco if they promised aid against Israel. So I doubt that changes.
So let's talk about Stalin's death. Was there anyone who would benefit from no Korean War? Was there anyone who IOTL improved their position BECAUSE of the war? The only one I can think of is Beria looks worse after the Korean War, so that's no great loss. But if it means an earlier consensus on Stalin's replacement, maybe it's not Kruschev, either. Thoughts?
Bottom line: the West feels a little better about their situation and about intervention in general, which could have significant butterflies later. The Soviets feel a little worse and maybe break early with the Chinese. The Chinese need a place to show they've arrived on the scene, and that's probably Vietnam.
