I have no problem with the coworker who takes the occasional mental health day, especially because we are chronically short staffed and our 2 floats are used to staff unfilled positions. With that being said, I have been on a unit where a coworker scheduled an elective surgery (conveniently) over the Thanksgiving and Christmas holidays and was out for 3 months. This was a chronic pattern for her. As soon as she came back I gave notice and moved on.
And yes... the supervisors or managers NEVER step up and help!