That is, what if the 1938 edition doesn't end up on the bottom of the Mediterranean in 1941. There are two possibilities here, neither of which is obviously favoured.
U-81 might not have encountered Force H at all, thus Ark Royal continues in service undamaged. This may not be as much of a benefit as it seems... the damage to Ark Royal showed up design shortcomings in British aircraft carriers.
Alternatively, she does take the hit, but damage control is started promptly - in OTL, Captain Maund decided to evacuate the ship to avoid severe loss of life should the Ark Royal sink rapidly. Effective DC early might have been enough to save the ship, but she's out of the war until repairs are complete.
Either way, the RN has an extra deck - and a famous one, afterTaranto and Bismarck - available for service. What happens next?