I agree. If London falls on Germany 2 or 3 (granted, 3 is a better option), it seems plausible that the game cannot continue. Why?
The cash, as I said before.
The transports are not wasted, they can be used to protect N. Africa (Landing in Morrocco for instance, with the Shipyard in Gibraltar, Germany’s still in a strong position with the fleet, now even threatening Washington DC and Ottowa) and to hold Scandinavia from Russia.
With no threat from the sea (and really, what possible threat do the allies pose from the see with no England to unit fleets and no air bases to hold planes and, of course, no place to set up D-Day) Germany has nothing to do but hit Russia and counter American fleet builds.
I do not think Germany even needs to take Russia. They just have to counter build and, IMHO, that means building 2 infantry for every 3 Russia builds. (Since Russia has no NOs to collect because of a submarine in SZ 125, this shouldnt be hard.)
So we are talking 60 IPC for Germany, per round, vs 40 IPC for Russia per round give or take. America is either building like mad in the Atlantic and thus losing the game because of VCs in the Pacific, or building significantly in the Pacific and thus not building enough to sink the Germans and liberate Africa/England.
All in all, I would LOVE for someone to prove me wrong, we can start the game on G4 after England falls, before Russia declares war using SOP builds, movements as a guide there are plenty of games to look at for reference on what should be where; but I do not think it possible for the allies to win any longer. Especially if you start with a Japan 1 Sneak Attack on Euro-American ships.