Churchill is still a figure of reknown but his legacy would firmly be in the Edwardian epoch rather than a WW2 character. Look at his history and he was an unremarkable schoolboy who became a journalist and reported on the Boer war, colourfully depicting it for the readers back in England and engaged in several dangerous exploits.
He joined the Tory party like his father (Lord Randolph Churchill), quickly fell out of love with it and joined the Liberals, then went back to the Conservatives. He served as Chancellor AND Home Secretary, presiding over important periods in British History.
Whilst his legacy wouldn’t be global, it would nonetheless remain fairly important to British History at the time as a stalwart representative of the dying off of the aristocracy and the rise of the “middle classes” in British politics during the 20th century.
I guess it would depend on what the POD would be – no WW2 without Churchill would probably mean he takes a minor role in the Government during the war period and goes around saying “I told you so” whilst writing his memoirs as well as his “History of the English Speaking Peoples”. An averted WW2 might lead to some interesting situations with the Empire – he would argue very fervently for no breaking up of the Empire and be very passionate about keeping the Commonwealth together as a cohesive political unit which could present an interesting future if vision were realised.
Churchill as most people know was a natural orator who could speak to the people in a language they understood and cultivated a good relationship with the media, Lord Beaverbrook in particular who was to become a strong ally. Churchill therefore couldn’t be relied to fade away into the background and will remain one of the main figures of the 30s and 40s.