Well, it is obviously difficult without knowing personal details to which we should not be privvy. It is more than possible the return to duty was justified, and that some underlying serpent leapt up and bit. We have seen the sad events many times in the UK where parole boards have assessed X as fit for release and X then goes on to commit heinous crimes. I have also seen (in military days) a premature return to flying duties due to manpower pressure with unfortunate results. I really do not think we should pry too deeply into this man's behaviour. The flight did not crash. Everyone got where they were going, albeit late, and it is said the Captain will not be flying again.
I do think however there are worthy questions as to the conduct of the crew, including the co-pilot/s and the way the airline handled the subsequent departure. The purser may well have needed some 'guidance' also, who knows?