Thon,
I don't think Stalin would escalate Korea. He surely knew about the massive disparity in nuclear weapons and he didn't want to rule an ash heap.
And there's the dilemma's horns.
If Stalin orders the North Koreans to accept a negotiated war's end then he'll be seen as having folded in the face of the West's "aggression." That will have huge implications for the Communist movements worldwide. It will have huge implications for Sino-Soviet relations as the Chinese poured huge numbers of their troops into that meatgrinder at Stalin's behest. A negotiated peace means all those lives - and all that risk - was for nothing.
If Stalin orders the war to continue then the pressure would mount for the US to do something truly decisive - as in making some Instant Sunshine™ take place over key targets in North Korea (at the least) and perhaps ones just over the border in China itself. The escalation spiral from that would be dangerous, yes, but it's one in which the Soviet's would lose an increasing amount the longer they let it run.
In OTL, the Soviets were able to avoid most of the damage that came with that negotiated end to the Korean war by essentially blaming it all on Stalin. Korea was "his" mistake and not the mistake of the Soviet Union nor of its new leaders.
In this ATL, I don't know which way Uncle Joe would go. Keeping the war going would risk those A-Bombs dropping. But Stalin might be betting that the West wouldn't have the stones to do that and that we'd blink first. That's a dangerous bet to be putting down.