Depends on the single event that led to their victory but you could easily argue that the British Empire would have been better off if it had never gone to war with Germany in 1939. Its a war that basically bankrupted Britain, caused the collapse of the empire, pushed Britain from being the major superpower into second division status, led to the dominance of its major rival (America), and has generally blighted the last 60 years of British history.

Humanity is better off because Germany lost, but Britain? Not so much.