This has been answered rather well before by /u/buy_a_pork_bun in this thread. Overall I agree with all of his assertions but in the end this is askhistorians. We deal in what did happen, not what didn't or might have happened. There's a sub for that I believe. /r/HistoricalWhatIf might be a better place to ask because any German victory in the east certainly would have required some very serious "What if"s.