It is not just about "theoretically" being outproduced.Agreed that historical variations should be possible (and encouraged, the idea behind the game is to play your own way, after all). That said, there's a decent chance that the US and UK could have out-produced Germany, Italy and Japan even if the USSR fell (as there would be a huge garrison requirement in a conquered USSR, and very little manpower and production advantage immediately following conquest) - the only real strategic long-term chance that the Axis had historically, outside of knocking the UK out early, was to get one of the powers to switch to their side (which I agree should be possible in-game).
That said, if it _doesn't_ happen in-game, and the powers line up the same way they did historically, then long-term, if the Allies want to fight until the end, even if the USSR goes under (which itself should be pretty unlikely) and aren't repeatedly completely incompetent, they will win, if the game has any sense of a historical strategic balance.
USA is on the other side of the planet, it`s logistics take a lot of man. It managed to produce a huge lot historically because other countries would fight for it.
Considering the loses that SU took and sustained, it is not even obvious USA and UK can put as many people in uniform, nit to mention supplying them. Historically US and UK were having problem reinforcing their armies in 1944.
If SU is out in 1942, the Allies probably need to draft at least another 15 million men, the men, they don`t have, not to mention the complication of landing against 5-6 millions of opposing troops.
I mean, let`s look at facts:
SU drafted 33 million man.
SU lost 8 millions killed, and probably many more wounded.
SU was maintaining 4-8 millions army in 1942-1945.
Considering the whole, can USA and UK supply about 4 times as many forces for battle of Europe, US only had 2,7m man in land forces in 1945, while, again, historically German Wermacht reached it`s peak at 11 millions in 1943, and allies would have take 5-10 millions of dead and keep fighting?
That is, questionable.