It is my "theory" that had this happened; Germany may have lengthened the war, but they would not have won it. No War against the Soviet Union would have allowed Germany to put more and more pressure on Western nations such as the United States and Britain. From 1941 onward 2/3 of the German army was fighting on the Eastern front. Had this not been the case, Hitler could have focused more on the War in Africa and operation Sea Lion.

However, despite the fact that Germany would have been able to devote all of it's efforts to the western front, the Third Reich could not have triumphed. The United States had more manpower, many more natural resources, and overall more economic might. One America entered the War, Germany was doomed, especially in resources. Despite wanting to eradicate Communism, Hitler also needed the Oil in the Soviet Union.

Therefore, I belive that Soviet Neutrality would have lengthened the War, not changed it's outcome.

Sources: The Third Reich at War By Richard Evans Wkikpedia

Note: This is My first r/askhistorians post, and I am also 14 years old, so this may not be perfect.