Also, if Britain did fall, I don't see them building battleships and carriers in Canada or India in significant numbers to come back and reclaim the capital... It'd be up to the US player to be responsible for liberating England.
I wonder what would have happened? If Britain fell in 1940 - would the US have gone to war about that? Who knows?
And if the royal navy had escaped - would they have been able to bring troops from around the empire to fight some way or other? It would have been a dramatically different timeline for sure. In WWI the UK was able to import large numbers of troops from around the empire. In WWII her relations with much of it were in doubt due to a growing sense of nationalism throughout it. Would the Indians have fought in 1940 like they did in 1914-1918. Dying on european battlefields far from home?
It's just too much too imagine.
Also of course; would the US have dared antagonise Japan - Germany's Ally if the British had fallen and Germany was 'all powerful on the continent?' Hadn't Britain and 1941 already proven that with perserverence the Axis could be beaten? In fact - the clear loss of the Battle of Britain by the Germans (though as said before - it was an impossible task for the Germans to win) was probably as great a propaganda blunder as a military one. The german armed forces - who had triumphed throughout Europe finally were halted. Equally important was they were halted in the most heroic way possible, by a bunch of disarmed islanders with nowt but a few fighter planes. The Battle of Britain gave birth to the myth of the 'Few' which alongside 'A day in Infamy' became one of the defining speeches of the early war years - the idea of the lhonorable insulted man who would grow in rage and power until those wrongs done him were avenged. Such examples would follow on land outside Moscow and in the Sea at Midway.
Whenever you look at the Minutiae of this stuff you can see the truth.
Battle of Britain:
Appears: Small poorly prepared airforce beats off massive war hardened airfleets 2 & 3 over the rolling green kent countryside.
Reality (in brief): Highly organised, well supplied air force holds its own due to advantages in range, radar direction, and aircraft qualities. Mixed with a heavy dose of attacker error (like attacking in the first place, and unrealistic aims and expectations).
Battle of Moscow:
Appears: After 5 months of blitzkrieg across the Russian hinterland, pulverising all before them, the evil nazis are stopped by the harsh winter, and the bravery of wives and children digging tank traps in the moscow suburbs.
Reality (in brief): Resistance to German forces stiffened markedly as the months wore on, and as soon as armies were destroyed so they were replaced. After German pissing about (thanks Hitler) many of the Panzer divisions were suffering mechanical differences before winter set in. Saving Moscow was an achievment - but with the help of Siberian forces released by Japans southern intent German defeat was guaranteed - even had they entered the city. The Soviets would not have surrendered after the loss of Moscow - they expected it and moved virtually all government out of the city.
Battle of Midway:
Appears: Well placed US bombers/torpedo planes catch Nagumo napping allowing a numerically inferior fleet to inflict the most important naval defeat (arguably) of the Pacific war.
Reality: Americans had been decrypting Japanese codes for ages. They knew about the types and numbers of planes and vessels in the Midway fleet, they also knew about the dramatic feint toward the Aleutians (which the won the Japanese two pointless islands!) If anything - a number of US planes couldn't find the Japanese that day which is a surprise! The Japanese sailed straight into the trap set for them - but unluckily helped a lot by laying our fuel and explosives all over the decks of their carriers <BOOM>.
Sorry... got carried away.