What would have happened if the Germans did not turn on the Soviet Union in 1941? They were allied before that and both invaded Poland together. What if they kept their alliance and worked together?
Then the Soviets would have expected the Germans to pay the huge bill for all the stuff they were supplying them with in 1940-early 1941. The Germans never paid, and they would have been very very hard-pressed to pay. Indeed, when the Germans invaded, the trade relations had reached a breaking point.
Needless to say, the Germans needed that stuff (oil, food, metals, rubber etc.) to keep fighting the UK.
That said, for Hitler that whole war business was for conquering fertile lands in the East, read Ukraine. So not invading the USSR would have meant he was at war with Britain for nothing.