Two slants on fatigue.
Earlier this year I phoned my ops dept at 0200 ish and advised I was not fit to fly. No questions asked, told to call when I woke to arrange transport home. Well handled.
I recall a conversation with an esteemed PPRuNer, who at the time worked under a FRMS. If I recall correctly, in his company all duty scored points, and the score of points then required days off. I seem to recall him saying that with judicial rostering, one could be rostered to work 365 days per year.