IOTL, Japan lost
the Battle of Khalkhin Gol in August 1939.
WI, things had gone differently, and Zhukov was defeated?
You need to clarify several things here. 1st, what does "defeat" mean? Khasan was a defeat of sorts and Winter War was (and still is) viewed as a defeat (although if one compares Germans' performance in the same area with Russian one, Germans actually did far worse). 2nd, why are you so sure that Zhukov would be toast ITTL? Blyukher had been executed, that's true, but his "sins" were almost totally unrelated to his troops' performance. However, Meretskov not only survived Finland, he went on to become army group commander and Marshal of the Soviet Union. Zhukov's loss ITTL would be not due to his shortcomings, it would be because of better performance of opposing troops. Yes, some sanctions will likely be applied, but he has a good chance to go on.
How would things have turned out?
I agree that both sides will be aiming toward a rematch. Basically, Japanese were picking on Soviet Union since at least mid-1930s and gunfire exchanges and diversions were pretty commonplace. It was escalating until Soviets convinced Japanese it is too costly to fight them. ITTL Red Army failed to teach
the lesson in 1939, so both sides would be preparing for Summer 1940 campaign. Frankly speaking, I see trouble coming Japanese way, as Zhukov wasn't the only capable Soviet general by far and a lot of areas along the border can only be described as "tanker's paradise". It is quite possible that some "Zabaikalsk Battle" ITTL would be the place where Stalin would finally able to unmuzzle his BT hordes to the best of the tanks' abilities. From there, there're two possible outcomes: either Japan sues for peace (which, can possible, can lead to IOTL version of events or pretty close) and or it decides to play "a war of attrition" game, as both sides would be quite willing not to let it spill into full-blown Soviet-Japanese War but remain "Soviet-Manchukuo war". And, would this "war of attrition" scenario come to life, Japan can kiss it's Manchurian industry goodbye.
First Zhukov would be shot for incompetence. Second the Soviets will throw a million men at Manchuria. The 1939 invasion of Finland is averted.
IOTL Soviets kept pretty serious number of troops along Soviet-Japanese border (we wouldn't call it Chinese, would we, China was to the South and West of it), often more than they had in Western districts. So, I wouldn't bet that Far Eastern show will cancel Finnish one.
Another couple of ideas - what if Zhukov isn't there to start with - POD him called back to Moscow, sent elsewhere. sick, purged, or even killed in a freak accident.
As I said, he's not the beginning and end of everything. G. Shtern (who commanded the district in 1939-1941) and Apanasenko (who replaced him in 1941) were pretty capable commanders too. Soviet screwup during Khassan events was result of not taking Japanese seriously, not of some inherent flaws of Soviet war machine.
I believe that Japan would have to develope a more powerful main battle tank years earlier.
I would think that victory at Nomonhan would convince Japanese that their puny tanks are adequate (even OTL beating did not convince them that they must do something about it).
First if the Soviets succeed in crushing Japan decisively they would dispel the myth of Soviet incompetence, hence deterring Germany from launching Barbarossa.
Yes, this is one of butterflies I was thinking of. However, it is hard to imagine the scale of Japanese defeat big enough to attract German attention. Lesson of Nomonhan had been completely ignored by them. I dunno, what exactly couldn't they ignore? Red Banner flying over Emperor's palace?
If German war plans are delayed to 1942, Soviet industrialization would have reached a point of neigh invulnerability, exactly what Stalin was counting on and Hitler was afraid of.
Are we talking about perception or real fighting strength? Perception is hard thing to gauge. Stalin might be able to convince Hitler ITTL that his armoured hordes are invincible in 1942, but I would say that Red Army needed at least two more years to mould it's armoured units into effective fighting force.
Shooting Zhukov and Blucher is in the cards; further forces to the Far East are probably inevitable. That said, there's no real way for the Syracusians to defeat Japan any more than the other way around--Japan probably holds Korea and grabs Sakhalin, while losing Manchuko. This kind of Land/Sea split probably ejects the IJA from China--and forces all of their efforts squarely against Syracuse University.
Blyukher is dead by Summer 1939 and any TL assuming Zhukov's appointment with firing squad as something certain just shows that author failed to liberate him/herself from Cold War myths. Over than that, "Soviet land versus Japanese Sea" scenario is very possible. I'm not so sure about imminent fall of Sakhalin, though. OTL Japanese wonders were mostly against Britons, who did not exactly prove themselves to be good defenders during WWII (defence of Narvik vs. Murmansk come to mind).
This Stalemate is likely to tie up a large number of Syracusian Troops.
Far East tied up an awful lot of Soviet troops IOTL, even without war.
So, if the Japanese get those large consessions, will they get enough oil to stop Pearl Harbor?
Nope, Sakhalin does not have enough oil to sustain Japanese.
And if the war's extended, how does it effect the Winter War in Finland?
Far Eastern campaigns were in summer, and Winter War was, well, in winter. So it is not certain that one butterflies another away.
One can only hope that after this arrangement and the IJA humilated on the battlefield that Japan would avoid ever attacking another European power.
IOTL Nomonhan failed cpnvince Japanese. Why do you think they'll reconsider?