If we assume that the Germans' 1940 offensive collapses (and/or the allies are able to mount an offfensive of their own) leading to a military coup, collapse of the Nazi state, and German armistice/surrender offer, the western allies have some big decisions to make.
In this context, it is important to remember that in 1939-40 the Nazis have not yet shown themselves to be radically different morally from ordinary nationalists and militarists. The vast majority of Jews in the west are still alive and the horrors in the east have not yet happened. The Allies are likely to see any German coup just an example of one set of bastards kicking out another.
(1) Do they accept any terms with a German regime in which the Army retains power or do they continue the fight for an unconditional German surrender?
(2) What does the West do about the Soviet Union, which is still technically an "ally" of Germany?
(3) What does the USSR do? Do they abandon the pact, declare war on Germany, and invade from the east or sit tight in their part of Poland to see what happens?
I tend to suspect that the West would be torn between a desire to completely demilitarize and dismember Germany (France) or restore a conservative Weimar-like Germany as soon as possible to serve as a counterweight against Stalin (Britain). If the French get their way, Germany may cease to exist as a unified state. In either case there would be considerable pressure to see Czechoslovakia fully restored - and possibly even enlarged slightly at Germany's expense. However, the anschluss may be allowed to stand in a peace which preserves Germany as a major regional buttress against the USSR.
Unless the Russians invade eastern Germany themselves, I would not be surprised to see a restored Poland under western protection, shifted to the west as in OTL.
I also suspect that in either case, a "cold war" of sorts would start almost immediately between the west and the USSR, perhaps leading to something more intense in a few years.
The USA would remain neutral, isolationist and militarily weak in comparison to OTL.
A war between the USA and Japan is still possible, but a Japan not in alliance with Germany and Italy may be much more cautious.
Mussolini would die in 1963 of old age as the highly respected "grand old man" of Europe
First, the French and even some British did not consider the Nazis to be anything "ordinary." The French wanted the Entente Cordiale to pursue a much, much harder line toward Germany, but was afraid to act unilaterally, for fear of estranging the alliance with Britain, and possibly allowing a better relation between Germany and Britain. After 1935 this is impossible, but the rearmarment has also started, so France and Britain have a narrow window between 1936-1938 to be able to achieve quick, total victory over the Germans and demand unconditional surrender. Although the French considered the Weimar Republic to be just a new set of krauts, they would have likely considered them better than the militant expansionist Nazis.
Secondly, do not confuse a non-aggression pact with a mutual defensive alliance. Neither Stalin nor Hitler had any intentions of actually assisting the other side in their wars in any way. If Germany falls, the Soviets are likely to pull another 1922 and isolate themselves behind their border again, until Stalin is confident that he can conquer a large swath of Eastern Europe quickly.
As for the partition of Germany, a possible case would be the abolition of the Anchsluss, the restoration of Czechoslovakia as a state in full (it couldn't get any German territory, adding more Germans to Czechoslovakia would just exaserbate the conditions that led up to the OTL in the first place.) France will probably demand and get the entire Saarland annexed directly to France, with no plebecite, and the creation of a Franco-British puppet government in the Rhineland (capital at Trier), but not east of the river. The Weimar Republic (capital at Frankfurt, so the Allies can be within easy reach if Germany goes wild again) is restored, but the constitution is carefully drafted by the Allies to allow no absolute rulers to ever again come to power in Germany. Germany is allowed to keep part of its military, but only as defensive divisions in the east to ward off a Soviet blitzkrieg.
Poland would be reformed as the German occupied-zone of Poland, with at maximum a small parcel of Upper Silesia thrown in. The Oder-Neisse Line is completely unacceptable to the Germans, so Poland would look nothing like it does in post-war OTL. If the Allies are feeling especially malicious, they will strip East Prussia from Germany and give it to the new Polish Republic. Poland will be garrisoned by Franco-Anglo-Czecho-Polish forces in case of Soviet attack.
In the case of Japan, the state of Germany and Italy will have absolutely zero effect on the decisions of the Japanese High Command. There was never a plan for their two Axis branches to assist each other, or to link up through India and the Middle East. If Japan, Germany, and Italy had never founded the Rome-Berlin-Tokyo Axis, Japan would have still invaded China in 1937, would have attacked the Allies in Asia, and might have even attacked Hawaii in 1940. Of course, with Germany easily routed, the French, British, and Dutch will be able to play a much, much larger role in the fight against Japan.