I think a Nazi victory over the USSR would be possible, but only under a very specific set of circumstances that arise not from one POD, but several. What it would essentially boil down to is this: Hitler acts smarter then he did OTL, and Stalin acts dumber. Hitler starts Barbarossa earlier in the year, without getting involved in Mussolini's misadventures in the Mediterranean. Also, he would need extra soldiers (not sure where those would come from, increased conscription, perhaps?). That way, if a situation like the Kiev Pocket arises, German troops can afford to encircle them and continue the advance anyway. Combining those two factors, Moscow could be taken. But they would still eventually lose regardless unless Stalin chooses to make some colossal blunders. Maybe in the wake of a Fall of Moscow, he might implement another series of purges against the military, eliminating whatever competent leadership remained. Or maybe he dies of an inconvenient health issue. Seeing as how Stalin was the one thing holding the Soviet government together at the time, his absence could lead to a very poorly-timed power struggle among the Soviet leadership (i.e., Beria/NKVD vs Red Army). And this would all need to happen relatively early in the fighting, with the Germans advancing beyond their OTL high-water mark by the winter of 1942-3 by the latest. Otherwise, it becomes a war of attrition the Germans could never hope to win. OTL, it may have taken the Soviets a while to get in gear, but once they did they were unstoppable. Other situations are possible too, but they're more abstract. A less industrialized USSR, a Nazi ideology that's more willing to tolerate various Eastern European nationalities, especially those ones which had little love for the Soviets (Ukrainians, Baltic states, etc.) So yes, Nazi victory was theoretically possible, but it was a very small window of opportunity that relied on too many factors that were out of the German Army's hands. If it wasn't too late already by winter 1941-2, victory was doomed by Spring 1943.