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[Once the Germans start heavily bombing Britain, and after they attack the Soviet Union, I doubt there is any chance at all this would work, so it seems this needs to be attempted sometime in June or July 1940.
Is there any chance at all that this could have worked?
I do not think so because fortunately Hitler was countered by a man who was as great as Hilter was bad. Here are some quotes from Winston Churchill from the times that you refer to:
"We shall not flag or fail. We shall go on to the end. We shall fight in France, we shall fight on the seas and oceans, we shall fight with growing confidence and growing strength in the air. We shall defend our island, whatever the cost may be. We shall fight on the beaches, we shall fight on the landing-grounds, we shall fight in the fields and in the streets, we shall fight in the hills. We shall never surrender!"
House of Commons, 4 June 1940, following the evacuation of British and French armies from Dunkirk.
What General Weygand called the Battle of France is over. I expect that the battle of Britain is about to begin. Upon this battle depends the survival of Christian civilisation. Upon it depends our own British life, and the long continuity of our institutions and our Empire. The whole fury and might of the enemy must very soon be turned on us. Hitler knows that he will have to break us in this island or lose the war. If we can stand up to him, all Europe may be free and the life of the world may more forward into broad, sunlit uplands. But if we fail, then the whole world, including the United States, including all that we have known and cared for, will sink into the abyss of a new Dark Age made more sinister, and perhaps more protracted, by the lights of perverted science. Let us therefore brace ourselves to our duties, and so bear ourselves that if the British Empire and its Commonwealth last for a thousand years, men will still say, 'This was their Finest Hour.'
House of Commons, 18 June 1940, following the collapse of France.
From this it should be clear that the UK was not considering at all to stop tehe war. most probably becasue they realised all to well that Hitler would be back as soon as he had gained more strenght.