Maybe England only had a few planes at the time. Not the point. The point was England still lived on to fight another day, no matter what or how, it continued to do so. No matter that they were not potent, they were not defeated. Leaving a wounded but not dead enemy behind you is always a poor choice. That being the historical reality, it was a mistake. True with Russia out, Britain would have had no real choice but to relent. However, in my mind, the reverse would also have been true. Had Britain been knocked out of the war, the United States would not have dared to interfere in a continental conflict and left Russia alone to face Germany. That removes the British military and lend-lease threats, as well as the American military threat, and it also frees up German divisions (perhaps not many) to be sent to the Eastern Front. With the extra focus, resources and men, perhaps it would have been easier for the Germans to accomplish thier goal of a quick victory over the Russians.

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Cheers,
Daniel