If it doesn't stem the tide, then an Entente Italy would still be a considerable asset for any WW2. With enemies on all sides and no relevant allies on the continent to speak of, Nazi Germany's chances of victory are much more clearly close to zero from the outset. Whether that would stop Hitler is doubtful, but maybe those initial years would not see all that many blitzkrieg victories. Or, maybe, the Entente stays firm with regards to Czechoslovakia - and Hitler is really discouraged. Weird, but not excluded. How Nazi Germany would trudge on without starting a world war is a difficult question, but France would be spared its defeat, occupation and destructions.