In my immediate family I have 3 people that have taken multi-year periods away from work for health reasons. Two are mental health related and the other severe arthritis. 2 of those 3 will probably never work again for the rest of their lives.

I've worked with a contractor that went into a coma during covid. Nearly half a year in a coma, then rehab for many more months. Guy is working now, but not shape.

I don't know the stats, but I'd be surprised if long medical leaves are as rare as you think.