People on here keep saying that 'managers should. . .' whether that is about hiring cover for sick colleagues or not expecting too much of staff. IME it really doesn't work like that. Whatever they 'should' do, it was always my experience that they didn't. If people didn't cover and do the job of others as well as their own, the constant threat of closing the department was brought up again, and it was a case of doing it or risk losing your job.
It saw me off in the end, after the same two colleagues had their regular 'stress' absences for months at a time, and I was covering for them. I cared about the students, so would answer emails on holiday in the evenings and at weekends, as well as having to write lectures for absent colleagues, cover their marking and so on.
I know it's unfashionable to say so these days, but IMO if people's mental health is not up to the job they should leave, and let someone who can cope do it, not expect colleagues to cover for months on end. Nobody minds doing a bit more for a week or so if someone has flu, but continually doing two jobs for the price of one is untenable. When people take 6 months off three times in 10 years, plus odd weeks here and there when they are certain that 'the system' will allow it with no loss of pay, there should be a way of getting rid of them without being accused of bullying (which is what happened when someone did try to 'manage out' one of my persistently absent colleagues).
It's all very well to say that I shouldn't have done the cover, but it just doesn't work like that.