F-35 Cancelled, then what ?

[Milo Minderbinder]

Stuffy
OK, lets take your question at face value and look at the options if the F-35B is cancelled
Assuming the decision is to maintain fixed wing you have two basic choices.
STOBAR
Catapult

If STOBAR the only available off-the-shelf aircraft is the Russian Mig-27K (the SU-33 is not in production) - assuming it works. I can't see the Russians letting us have those, and there may be a few other political problems....
Of the other possible aircraft - Typhoon, Griffin, Rafale, for all STOBAR is a pipe dream, years away if ever.
I suppose you could buy a few prop driven COIN aircraft and just use the carriers for bush wars......but that would hardly be efficient use of them.

If you want catapults then you have several options
You're right in saying the turbines and diesels won't produce steam, but in theory there were going to be spaces left for steam generation gear. Assuming there really are, you'd have to cut the ships open to fit multiple steam gennys, fit miles of high pressure steam pipes and massively rework the beast
Or you could go cap it hand back to General Atomics and ask for a new slot in the EMALS supply chain. But that would mean a delay until (I guess) 2025 and the problems inherent in the design are still there.
Or you could go back to Converteam (Alsthom as was) cap in hand and ask them to restart the cancelled EMCAT system. But as Converteam are now USA owned I think we'd get a USA-government instructed rebuttal, even though the work would be in the UK and France
Either of those two electrical systems would require heavy engineering to the deck, and radical redesign of the ships electromotive propulsion system.
Or you could go down the madcap route of ICCALS - "Internal Combustion Catapult Launch System" - which is exactly what it sounds like and would need combustion chambers to restrain the explosions.

The choice of aircraft is irrelevant. It could be F-35C, F-18, Rafale. The problem is, whatever is purchased theres no way of launching them without massive construction delays and massive remedial work to the vessels.