When I was a student teacher, my mentor teacher had a hard time letting go of his classes so I could develop my teaching style. Weeks in, when I felt I did little more than make copies, he needed surgery, keeping him out of the classroom for two weeks. A substitute teacher was required, but I didn't let him do anything.
The teacher returned, but still couldn't talk for another week, so he watched me run his classes. When he was better, the teacher acknowledged that he had a hard time losing control of his class, and that the surgery had benefited both of us.
I'll keep your story in mind if I ever decide to take on a student teacher.