So what it sounds like is Germany did not have the manpower nor resources to win World War II. Even if they did "defeat" Russia they would have been mired in a years long guerrilla warfare campaign with Communist Partisans which would have numbered in the millions while also attempting to stave off a superior British Air Force and Navy and a massively industrialized United States. We also have to consider what constitutes victory in Russia. Most people assume it would have been the taking of Moscow but there was no indication Russia would have surrendered into submission if the Germans did manage to take the capital and the losses to do so would have been incredible. The Russians were always fighting a battle of attrition with the Germans and they were always going to win eventually, even if the Germans managed to take the Caucus oil fields. It just would have prolonged the German war effort but in no way, shape or form guarantee them a victory.
America still would have developed the atomic bomb and instead of dropping them on Japan would have used them on both Germany and Japan as there were plans to use the bomb in the European theatre anyway but by the time it was ready Germany was already on the floor for the ten count. Germany managing to take the Russian oil fields or Moscow would have only made an already bloody conflict much worse given their renewed ability to wage war but they didn't have the tools in place for an ultimate victory. As long as Russia and America are in the picture Germany cannot win the war.
That's not how wars work breh, or at least worked (the advancement in weapons tech has changed the landscape completely). there were millions of french people in France yet Hitler managed to lock their country down. Even if resistance exists, it can hardly do anything substantial without the coordinated efforts and/or backing of a "government", this is easily observable anywhere else in the world where a civil conflict exists, hence the opposing side to whatever government pretty much usually resorting to "guerrilla warfare". People tend to think of numbers as a decider, yet here we have Germany, which in many regards hadn't even fully recovered from WWI and the sanctions imposed on it, having the world shook. Not even tech is a decider (the U.S knows this due to nam and afghanistan), yes the british had superior air force but the air fields bombings rendered that advantage almost obsolete for large parts of the conflict.
The taking of Moscow would have immediately been followed by locking down strategic points, routes, and military bases as well as production sites, and a puppet "russian" government would have also be installed to assuage the populous. this isn't mere speculation neither, its exactly what the nazis did everywhere else, look at Austria, Czechoslovakia, France (he split France in two with the germans occupying the north and placed a phoney french government in the south "Vichy France").
If the Soviet Union had fallen, eventually so would Britain in the North of Africa and then the West because Hitler would have had fuel, supplies, and machines to commit to the North African front like his generals advised and then it would be a question of time til mainland Britain fell too, as they would have choked out supplies from the commonwealth. hell,
Churchill had already been deliberating about suing for peace.
Hitler saw the British as an expansion of his "aryan" ideal. Hess, Hitler's deputy, said that
"Hitler had great respect for the english people". Nazis often attempted to recruit British prisoners of war to their side. Eventually, some British POWs volunteered to fight for the nazis and formed a small waffen-ss unit called "legion of st. george" (this is another thing that's often overlooked about Hitler, he was demonic but charismatic, that's how he rose in the first place, dude studied which looks, poses and voice tones would have had the most impact on people when he was locked up, and every country he absorbed, he managed to sway substantial numbers to his "cause"). Secondly, Britain is an island or achipelago, it makes potential ground invasions time/weather sensitive (keep in mind that weaponry and logistics at the time differed from what we have currently), and their Air Force was nothing to fukk with, especially if you were going to commit ground troops. Thirdly, he feared that if Britain was to fall, part of its empire would have fallen/ended up on U.S' hands (tensions between U.S and Germany had been growing since Hitler made a move for Poland, and forced Britain's and France's hands). His beef with Britain wasn't really that serious (hell, when he first started making moves and annexing land and introduced military conscription to grow his forces many times over what the
"versailles treaty" said germany was allowed to, he seduced both england and france into the
"munich agreement" with different conditions), that's why him and Goering decided to change strats from bombing air fields to bombing cities, and later tried to siege. They wanted to force London into suing for peace so they could focus on the Soviet Union.
contrary to popular belief, the U.S weren't the military boogeyman back then that people like to think they were, the conflict expedited the growth of the U.S military industrial exponentially, and that included the manhattan project/atomic bomb, but the nazis were close to reach it too, and they had their wunderwaffe weapons program which had to be rushed due to fighting on so many fronts. Had Soviet Union been consolidated as German territory, it was gonna be halloween for us.