I think it's fair to say that if F-35B is cancelled the RN will lose both carriers. Too late to change spec again and even if it wasn't the added delay and cost would see it abandoned as fulfilling none of its raison d'être. So the best hope our dark blue FW aviators now have is -B.
Having only one jet type that could use a STOVL ship certainly removes all fallback options for SDSR 15. Someone has played a blinder if this was 'as intended'