I think the key will be whether or not the doctor agrees to his version of events, saying the patient was advised to take a holiday by them.
That’s pretty standard advice though- exercise, rest, relax, do things you like doing, get away from the problem, etc etc.
Pure speculation this, but after 8 months there’s a pretty good chance that one or both parties had given up on returning to the role he left. After about 2 months, I knew I wasn’t going back unless things changed drastically, so the rest of the time was spent a) establishing that wasn’t going to happen and then b) looking for different work in the company. And if that hadn’t worked out, it would have just been c) wait til the end of the contractual sick leave.
So… My assumption, is that the charity didn’t want to wait that long, and thought they had an opportunity to cut it short.