I still do not see how it would have been possible for Germany to defeat either GB or Russia.
Stalin was prepared for a long, bloody fight and moved his armament production to factories on the other side of the Urals … about as far from Moscow as Berlin is from Moscow. Considering the difficulties that the Germans had in approaching Moscow, can you imagine any way it could have been possible to make it to beyond the Urals with losing vast quantities of manpower just to hold the territories from partisan uprising? Most of the German advance was gained by their catching Russia off guard. Yes, had Moscow, Stalingrad and Leningrad been taken the USSR would have been less able to fight but still that isn’t victory for Germany. The best Germany could have hoped for (once it became apparent that Russia was not going to collapse) would have been to pick a defensive line and stabilize the front. Difficult to do with a defensive line thousands of miles long. Ask the Japanese about their experience in China where they had hundreds of thousands of troops tied down in a similar situation against a country with no factories in the far distance to help build war supplies.
Likewise, Churchill was no less determined. The German Navy could have no hope of either invading or starving Britian as the British navy was too dominant. Only if the ME262 was available IN LARGE NUMBERS in 1940 could air superiority been maintained such that an invasion would have been possible (but I think still very unlikely to succeed), but this aircraft was never available is sufficient quantities. And then what to do if GB continues the fight from Canada?
I also don’t buy the idea of fortress Europe as not being possible to invade. We did it during the war in the amphibious invasion of Sicily and Italy. Africa and the Middle East is close enough to Europe for this type of operation against Greece and Vichy France as well. And had Germany won in Africa, it would have been possible to take Africa back from India, via the Middle East.