2. The German endgame was always conquest in the East, so even if the Brits DID throw in the towel the conflict wouldn't have ended. On the Eastern Front, the Germans were overstretching their offensive capabilities and logistics barely 6 months into the war (hence why they failed to take Moscow). Pivoting additional forces freed up from containing the British Empire wouldn't have helped Germany's logistical problems, so they wouldn't have forced a surrender on the Soviets like they wanted in any circumstance.
I highly recommend reading Wages of Destruction. For a more accessible study of WW2, check out "Military History Visualized", an Austrian military historian on Youtube who uses a LOT of primary sources.
My current source is the relatively new economic history of Nazi Germany, The Wages of Destruction by Adam Tooze (http://www.amazon.com/The-Wages-Destruction-Breaking-Economy...). It's very good, and shows how economics were vitally important from beginning to end.
E.g. part of the motivation in invading the Soviet Union was to address the crippling loss of productivity in their "Greater Western European Co-Prosperity Sphere" from the end of British coal imports. They needed to get enough food to the miners of the Lowlands etc., and the scheme was to starve the USSR cities and redirect the agricultural surplus east. Of course it didn't work out, but they did have a plan that wasn't entirely irrational.
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