Lets say Japan waited to see if Russia would be knocked out and when that doesn't happen they decide on neutrality. So I guess Japan could come into alliance with the US and Britain. Churchill would love this as Japan would adopt a pro-colonial policy to preserve their gains in China.
No oil embargo then?
OTOH, this will sour relations between the UK and the US: a lot of Americans don't like Japan at all, and don't like the idea of their grabbing control of China, either. (Also, the longer the Japanese continue trying to subdue China, the more Chinese society is ground into dust, the better for the Communists)
As far as the Italians go I see the war stalemating in North Africa with Italy dropping out of the war when the Soviets advance into Berlin. Mussiolini then forms an alliance with Churchill and De Gualle(or whoever ends up in power in France).
No doubt, although it's going to be an uneasy alliance: France and the UK can't afford having Italy go commie, but it's sorta hard to forget that Italy was fighting on the other side quite recently. OTOH, with the Red Army right on his border, Musso has no choice but to take whatever terms the French and British care to give him in exchange for an alliance: Musso probably isn't getting Ethiopia back, for one thing.
Nukes will be along shortly: with the US not in a war, there will be no US project on the scale of the Manahttan project before the war is over, but the UK was working on their own project, and basically handed it over to the US in our history because they couldn't afford to run a program and fight a war at the same time. In this TL, they probably put more money in it once the war ends, and may cooperate with the US, depending on how quickly the US moves away from "not our problem" to "OMG, THE REDS ARE ABOUT TO OVERRUN ALL EUROPE OH NOES!!" In any event, the bomb should be along within a few years - and the USSR will have it not long after that, thanks to their fine spy program and their not untalented physicists. One wonders how many Germans will be worked to death doing the crap work, handling Plutonium, etc.
Alas for the desires of some posters for genocidal bloodshed, a preemptive war in the short interval when the UK and perhaps US have bombs and the Soviets don't is unlikely: it takes rather a while and a lot of money to build a mass-scale bomb production system, and most US politicians, oddly enough, lacked the clear preception of modern right-wing bloggers that the way to deal with a possible future threat is to kill hundreds of thousands or millions of innocent people now.
Americans may feel less confident about their ability to change the world and in their own power. After all, the USSR and UK won the war without US help, and perhaps the atom bomb is more clearly a UK/US joint project rather than being as US-dominated as OTL. Also, the lack of a Korean war will help keep US bellicosity at a low ebb. Also, the USSR is probably going to be less pushy than it was OTL: there is no divided Berlin to act as a source of friction, there is no danger of Germany being rearmed as a western weapon, and the human losses, worse than OTL, will discourage any adventuring.
Of course, some things may change this. If an economically exhausted Japan withdraws from China (aside from Manchuria, mayhaps) and it goes Red, people will get rather panicky - and then there is Germany.
The Holocaust Deniers will be active from the start in a world in which all the deathcamps are liberated by the Soviets, and the US will be more sympathetic to Germans which they never were at war with. And the Soviets will be harsher on Germany (and Austria) than in our TL, since they don't have to worry about the impression they are making in a larger W. Germany (rump Rhinelands Germany isn't going to be much of anything for quite a while). A lot more executions, a lot more deportations -
millions of Germans may be exiled to the USSR proper, to work as slave labor cleaning up the damage their countrymen inflicted. Rape, looting, starvation, corpses constantly floating up on the west bank of the Rhine as they are shot trying to flee across the river - the impressions will be nasty.
I'd expect that Stalin will ease up in time - you can't run a whole country like a gulag, and Germans will fight back out of sheer desperation and in hopes of inviting a US/UK intervention - but by the time some functional regime has been put in place and the killings and starvation come to an end, the anticommunists forces in the West will have adding a lot of new stories to their fundamental anti-Soviet texts.
Eastern Europe, probably not too different from OTL, although Finland may end up being incorporated into the USSR or at least communized in this TL. Poland: incorporated into the USSR? Hard to say: Stalin, at least initially, is going to be less concerned about making a good impression, but OTOH there still is the US to worry about, and Poles have never been particularly quiet subject peoples. Stalin may not be satisfied with letting Tito take over in Yugoslavia, and arrange for someone more dependable to take his place.
More thoughts later, perhaps.
Bruce