What changes if the Taranto raid loses all its aircraft and damages no Italian battleships?
Short answerThe Italian fleet remains at full strength, and the Royal Navy probably tries again by another method instead of enjoying a temporary numerical advantage.
NotesThe aircraft in the premise need correction: Swordfish, rather than Spitfires, conducted the raid. If every torpedo bomber were lost without damaging an Italian battleship, the Regia Marina would retain its numerical strength. The Royal Navy would likely organize another attempt with Swordfish or a different method. Until then, Britain would operate without the roughly three-month reduction in Italian battle-fleet pressure created by the historical success.