You're partaking in some serious historical determinism. The UK was pretty much a hair's breath from starting peace negotiations post the fall of France. Lord Halifax was the favorite to succeed Chamberlain and personally wanted to begin peace negotiations through Mussolini. The American ambassador to the UK at the time, Joseph Kennedy, also urged the British to seriously consider peace. For the eastern front the Soviets were very close to breaking and were actually in secret peace talks with Germany from 1942 to 1943. With or without the UK out of the war in 1940 it is possible for the Soviet Union and Germany to have agreed on a peace with would see Germany gaining a stronger foothold in eastern europe.
Of course the question becomes what the consequences would be of a European continent dominated by Germany, but which would still have the UK to its west and the Soviet Union to its east seeking vengeance.