My theory is that if Hitler took Moscow, Stalin gets deposed and a new non-Bolshevik government takes over and rallies the country to victory.
Probably followed by another Russian Civil War. But that would have been the best-case scenario for us.
It’s a fun game. Italy takes Greece quickly. Germany takes Russia quickly. A stalemate then a negotiated peace that frees France. Followed by a Cold War against the Reich with nuclear proliferation almost exactly the same as the real one with USSR only the bad guys would have cooler uniforms. It is like playing Risk.