Ivan - I think the only chance would be if one of them somehow found out Stalin was dead before the others and had time to plan any necessary purges and put himself into the best possible position before Stalin being dead is known by everyone. For example Beria is summoned to visit Stalin and finds him dead but tells the guards and everyone else that Stalin is ill and ordered not to be disturbed.
Otherwise as you said no one was in a strong enough position to easily claim and hold power.
Now I'm curious as to how the rest of the war turns out, and if this turns into an all out Nazi, or even Axis, Win. Somehow, I expect the PoD is too late to prevent Pearl Harbor;* what can the "Allies" (which TTL are pretty much the Commonwealth and the US) do now?
*(Sakharin possibly being easier pickings notwithstanding)
If the USSR collapses and and the UK hangs in the war and Pearl Harbor happens and Germany declares war on the US I would think the UK would then decide to stick it out. Germany would still have a lot of work occupying the vast amount of territory they captured. If they decided to start building an amphibious capability to invade the UK that would take them awhile and meanwhile the US would be reinforcing the UK and building up their Air Force. I don't think the Germans would be able to obtain air superiority to ever make it across the channel.
On the other hand DDay happening in 1944 doesn't seem likely either. The US/UK would probably eventually win in North Africa by overwhelming the Germans from both sides after an Operation Torch event happens. The Germans would be able to put more resources into the Luftwaffe and air defense which would make the allied bombing efforts more costly and less effective. The Axis would be able to put a lot more forces into France and Sicily and other possible invasion points, so I'm not sure what the allies would do. They could wait until nuclear weapons were available, however German air defenses would be much stronger than Japan in 1945 so they would probably want to wait until they had multiple bombs and then plan a large raid with lots of aircraft to ensure success, so I could see the war drag into late 1945 or 1946. But as long as the allies decide to stick it out they should eventually win since the Germans were so far behind in their nuclear programs.
The best the Germans could hope for is the US/UK to grow tired of the war before they have nukes and accept a peace treaty and enter into a cold war.