I just found some pictures of the terrain which illustrate why it was ASB for Japan to win a battle near near Khalkhin Gol without tanks or good anti-tank weapons
http://forum.axishistory.com/viewtopic.php?f=65&t=147360. Unfortunately as we diverged into the problems of achieving such an improbable victory (and Syracuse University), we never came near any conclusion on its consequences.
Two posters favoured a quick rematch
Stalin would never tolerate the USSR to be seen as weak internationally, to have made no progress since the defeat of 1905. It would embolden further Japanese aggression in the Russian Far East, not to mention Hitler.
First Zhukov would be shot for incompetence. Second the Soviets will throw a million men at Manchuria. The 1939 invasion of Finland is averted.
and
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.
One counter argument is simply that Japan would need a way of defeating Soviet tanks to win in the first place. One difficulty about alternative history is that there is generally no agreement about the situation after the POD. Thus
I don't think Stalin's going to be that rash.
Makes sense if the Japanese have shown greatly increased fighting power (for example deployed over a hundred type 4 Chi-To tanks!) but is less plausible if the battle was lost by Soviet incompetence. Either way, Stalin would want to focus on Europe, especially after June 1940, so any rematch has to be quick.
Thus we diverge into two possibilities. One is a massive Soviet attack at about the same time as the Winter War. As Stalin underestimated Finland, I do not see why there will not be a Winter War even if there is a simultaneous attack in the East. What will be the result of a late 1939 August Storm? The problem for prediction of a result is again that Japan has to have better anti-tank arms for the POD but how much better? However there are also diplomatic consequences. How will Japan's relations with Britain and America change if the USSR is at war with Japan and Finland?
If we assume no immediate Soviet attack but do not skip quickly to June 1941, we can ask how Japan's politics would change during 1940. There is a lot of literature on the Navy and Foreign Ministry's views on the Tripartite Pact but it is normally just said that the Army was in favour. Why? Would a victory at Khalkhin Gol have changed the Army's view?
Finally
A lot differently as it would be a victory for the Japanese Army and they might decide to go in the opposite direction resulting in no Pacific War. Zhukov would presumably be liquidated.
In 1941, Japan and Germany decide to attack Russia with Japan aiming to take control of Siberia. American stays neutral and Britain seeks peace being allowed to retain the bulk of the Empire although Japan may want a share.
Plausible if there were no worries about oil and other raw materials. However, would that be the situation? Seems to depend on USA -Japan relations up to June 1941. What I never understood is why Japan did not use the year from June 1940 to move most of its army from Manchuria to China and try to take Chungking. Would that be more likely in this POD?