1) Hitler and Stalin were never going to be 'allies'...Eventually one, or the other would have turned on the other.
2) No matter what Sea Lion wasn't going to work. Germany just didn't have the Navy, didn't have the landing craft for the landing, and didn't have the Navy/ships to keep supplying an Army in England, if it made it. I could see so many German divisions maybe making it to England, but then getting stranded. Also IMO Hitler was never really 100% committed to invading England. Actually I don't he think really wanted anything to do with it, but France fell quicker than anyone anticipated, Goering told him the Luftwaffe could easily defeat the RAF, and England too would be a cake walk.. Even without a 1941 invasion of Russia on his mind I think eventually though Hitler would have had 2nd thoughts.
3) By August 1945 none of it would have mattered.