Lemme get this straight: so you´re expecting an F/O (intimitdated through a ´the show must go on´ company cuture) to say "gime the tech log old, ´cus I wanna ground this aircraft?" You gotta be kidding!!! Even in EZY (which is according to the Brits ´supposedly´ better than Ryanair) F/O´s rarely get to touch the Tech Log, let alone make an entry in it!
I don't condone what the Captain did. Even if he resigned I'd still sack him.
I agree that preventing someone behaving erratically in the air could be close to impossible. On the ground is different.
The F/O knew there was a defect with the aircraft and has a duty to report, first to the Captain. If the Captain ignores it, the duty to report does not go away.
The F/O was prepared to get back in an aircraft he knew needed an inspection with cabin crew and passengers and a Captain who had recently shown scant disregard for SOP's, the AOM, CRM, airmanship etc. I'd be tempted to sack him also, he's not there for ballast!
F/O's need to know what they would do to break the chain of events unfolding and if they're not prepared to act why do they bother turning up ??