a possibility that England would sue for peace rather than fight an unwinnable war against Germany
That's different than what the discussion topic suggests...that Britain does not enter the war at all. I can't see that happening, but Britain suing for peace after Dunkirk is certainly within the realm of possibility.

However, there's still the Far East, and Japan is going to eliminate Singapore when it takes the DEI...they simply have to for strategic reasons. Then what? Granted the alliance between Germany and Japan was mostly a paper affair, but what does Germany do when Britain is forced to declare war on Japan? I can't see them not doing anything to hold up their end of the alliance