it's impossible not say we would have lost the war without Churchill we had many other military leaders. considering new played a pretty minor role in the second world war it's a bit of a stretch.
When Churchill took over Chamberlain and Halifax were already in touch with The Italian Government asking if Mussolini could broker a face saving deal with Adolf.
It was only the fact that at that moment the Italians invaded Abyssinia that stopped them doing it.