there was no way for Hitler, from the shores of France, to impose his will on the British.
Further, the empire at the time was a source of manpower, not a manpower constraint. And Churchill always knew they need only stall until the US entered the war. I also don't think the UK being "out of it" dramatically changes the equation on the eastern front. The eastern front was not the "near thing" made out by reaching the outskirts of Moscow. To achieve that the Wehrmacht had exhausted its ability to further conduct offensive operations. Any further steps would include penetrating the defenses or encircling a city 10 times larger than Stalingrad and facing the still fresh Mongolian divisions, while being 2000k from their supply and no reinforcements. That just isn't "almost", it is overextended.
US preparation and the US might that would have allowed for greater will on the part of the UK to rejoin the effort. The US was much more likely than in 1914 to join the war, and was already preparing to be able to conduct operations that would not have included having Great Britain as an island fortress. They began the B-29 program prior to entering the war. It was the most advanced and expensive weapons system designed to that date, and that includes the Manhattan Project. In the summer of 1940 12 Essex class carriers (already designed) were ordered by Congress.
Again I contest. If there was no way for Hitler to impose his will on the British how could the British impose their will on Hitler with no army. They may have had the empire but were these trainable troops? - the Aussies and the New Zealanders were great but few in number and they went home to fight the Japanese. All the millions of empire manpower in India did not prevent Burma falling and whilst they did help liberate it that was 4 years later during which time the British expected the Japanese to invade India whom was making noises about not really liking the British too much either.
With the UK surrendering part of the price would have been Axis troops on the Suez canal and probably a few British colonies - definitely protected access to middle eastern oil. . No need for long drives to the Caucasus. All aircraft and anti air units available for the Eastern front - much fewer occupation troops needed in France, Norway and Mediterranean. 25% of armour NOT diverted to North Africa. No wasting effort on warships and submarines and the Kriegsmarine. And assuming the US didn't enter (why would they with Japan to fight and no ally in Europe?) no lend lease to the Soviets who's armies at one point were receiving at least one meal a day from the US plus virtually all their boots, trucks and tires.
Russia was too big to conquer entirely but they just needed a secure grip on the Western half and its communication networks (i.e. Moscow and its railway hub) for long enough to dig in properly, fix the railways and build some better roads, get proper shelter for troops at which point I doubt they could have been moved till the nuclear bombs arrived