Stalin being couped is pretty much a no go. Everyone was too afraid of him to attempt it, and they knew that in the middle of a war it is too risky to change horses. However if Stalin dies of natural causes some sort of collective leadership (probably with Molotov in charge) would take over. They would give the generals much more leeway, both because they lack Stalin's personality defects and their position would be too precarious to micromanage the war. The war probably goes worse for the Soviets at first, but they might do better without Stalin leaning over everyone's shoulders.
I think Zhukov would soon find himself more equal than others, if not in formal title than in actual power. Beria doesnt last long as he made too many enemies. And assuming he "saves Moscow" like he did OTL, it would be hard to limit Zhukov's popularity and his power. You could a Soviet version Washington, Julius Caesar, or Napolean. It might have happened OTL had Stalin not been so aggressive a boxing him in with Chuikov, Timoshenko and others.