Due to Hitler insisting on invading Russia during winter...I think the Russians would have done fine on their front by themselves.
It was just way too big an area for Germany to control really.
Reminds me of that line from the Princess Bride,
"Never get involved in a land war in Asia...but only slightly less well known is this - Never go up against a Sicilian, when death is on the line! Ha ha ha ha ha! Ha ha ha ha.... (thud)"
That's a great movie