We are talking about a German-Soviet ARMISTICE!
Of course such an armistice does not prevent the Allies from supporting breakaway regimes in the Caucasus and Transcaucasus to keep the Caucasus oil out of German hands.

Such regimes could be supplied from Iran and there are plenty of Armenian emigres in the United States who would be happy to help liberate former Soviet Armenia.
Which is to say that especially as many anti-Communists as there are in Washington, the Wallies will not allow any repeat of the Treaty of Brest-Litovsk. The Soviet Union started World War II as an ally of Nazi Germany. Then Hitler attacks the Soviet Union and suddenly the USSR is an ally of the West. If the USSR sues for a dishonourable peace and becomes once again an ally of Nazi Germany, albeit with reduced territory east of the Volga, it is still Communist even if it is not engaging in active hostilities and thus, still an enemy of the democratic capitalist nations of the West.
So don't expect the US to respect the Soviet Union's withdrawal from the war, especially since treating the Sovet Union as an enemy makes it legally possible for the US to invade and occupy places like Petropavlovsk-Kamchatsky or northern Sakhalin that could be strategically very valuable in the war against Japan.
Or for that matter, Murmansk, and Archangelsk with a quick move to occupy Karelia, and Archangelsk and Vologda Oblasts as a prelude to taking St. Petersburg, knocking Finland out of the war and reopening at least a northern Eastern front against the Nazis. The French and the British may not understand how to keep engines running in bitterly cold weather, but American forces, engaging in maneurvers in Ft. Riley Kansas, Camp Carson, Colorado, Ft. Warren Wyoming, Camp Malmstrom Montana and Ft. Snelling Minnesota will learn to operate in cold tanks and trucks in cold weather as many have already learned in civilian life --perhaps even better than Russians, since more Americans at that time HAVE cars and trucks.
And if the Germans have damaged Stalin to the point that he is forced to seek an armistice, can the US finish Stalin off, perhaps with naval flotillas up the Ob, Yensei and Lena Rivers during the summer of 1943 that take the cities along the Trans Siberian Railroad while effectively occupying the rest of Siberia with smaller numbers of forces in order to preclude the consolidation of a Eurasian Berlin-Sverdlovsk-Tokyo Axis that would have much of it's industrial production in the heart of Asia in places like the Kuznets Basin (Novosibirsk) out of range of even B-29 bombers the US is developing? One would think that preventing such an axis would be a US -Western Ally defense priority.