Is the author here not requesting a WI regarding Churchill and Reynaud's dealings with Germany rather than a discussion of how Germany could have been defeated militarily with a POD of early 1940?
1940 and 1941 sees grinding attrition, and the Allies begin to turn the tide. Germany runs low on resource,s as Stalin alters their agreement. He probably makes another go at Finland, or moves towards Turkey.
I doubt Stalin would trade the prospect of a war against a crumbling Germany which carries the rewards of controlling the rest of Poland, Czechoslovakia and perhaps eastern Germany for a relatively backwater former province of the Russian Empire or even better control of the Black Sea and a gateway into the Middle East through Turkey. The latter two are opportunities which not only will continue to exist after 1941, but perhaps may be facilitated even more easily as Soviet public morale will increase after a short, brutal and successful war with Germany and the military will regain confidence, not to mention perhaps frightening the governments of those nations into a somewhat more submissive role.
As a result, I would state that it is highly probable that the Soviet Union would invade a collapsing National Socialist Germany - though when in 1941 and to what extent they'd advance to I am unsure of, but even just capturing the rest of Poland, Eastern Prussia and the Slovak Republic yields some fairly attractive centres of industry and commerce, not to mention technology, which can be gained without a war of attrition and massive casualties.
British and French revanchism would be lessened with a quick, decisive war (compared to the First World War and OTL) and a rapidly encroaching Soviet Union. Territorial integrity of Germany would be preserved, the National Socialist party would be disbanded and a number of the most senior leaders (including Hitler, if captured) are executed for war crimes or imprisoned for life, the SS, the mostly redundant SA and any other political and paramilitary arms of National Socialist Germany would also be disbanded, but for the most part it would be a less harsher version of the Treaty of Versailles. Germany would most likely be allowed to retain the Wehrmacht at full capacity in order to provide a bulwark against the Soviets, though the Kriegsmarine would be heavily reduced and the Luftwaffe may or may not take a reduction too. I heavily doubt that any technological restrictions would be imposed on Germany other than maybe chemical and biological warfare which Germany did not resort to on a large scale OTL anyway.
As to territorial concessions imposed on Germany, you could see some very small border changes in the favour of the allies on the Danish, French, Belgian and Dutch borders, but most likely not to the same extent as OTL and war reparations would be less severe in order to not make the same mistakes of the Treaty of Versailles and prop up the nation against Communism.
Regarding whether Hitler would be overthrown, well, it's certainly possible and a lot of assassination attempts did come close, but it all depends on how it is handled. It is likely that a short civil war might break out, helping Britain and France sweep through Germany even more easily and cause a conditional surrender when they cross the Rhine from a new German government? Otherwise, they may just have to enter Berlin to unseat the National Socialists.
The very interesting prospect is whether the Soviet Union would halt once the National Socialist government has collapsed and a new German government is instated or not.
Perhaps Stalin sees wisdom in securing his conquests and absorbing them, or perhaps he'd rather press for more of Europe and concessions from the Western Allies seeing as they would have been weakened by two years of war?
