Yeah, there's a lot of factors and variables to calculate. We can never know what could have happened, only speculate on it. Personally I think that Germany could never capitulate the UK nor the US. Maybe they could try something on the UK if they did develop nukes earlier than the yankees and capitulated the USSR...

But even then, knowing very well what nazis do to communists and Slavs, the USSR would fight to the last person to win. I don't think Germany would ever be a par with USSR's manpower, industry and military genius (of course they got beaten hard in the first two years of war, but they managed to comeback). I think even on a 1v1 Germany would eventually lose. Idk.