Stars like Zach Braff leave due to burnout, departing Scrubs to take a break from TV.
Some actors exit to pursue opportunities, like Jennifer Raine leaving Call the Midwife for US roles.
To explain absences, characters are killed off like Rayna Jaymes on Nashville.
Main roles often recast, like Ashton Kutcher replacing Charlie Sheen on Two and a Half Men.
Shows change format when leads depart, as The X-Files did without Mulder.
Continuing without a main star can hurt ratings, like The Office minus Steve Carell.
Main stars sometimes return as guests, like Carell’s finale cameo on The Office.
Actors leaving over creative disputes, like Connie Britton’s Nashville departure.
Some stars exit over dissatisfaction with roles, like Farrah Fawcett on Charlie's Angels.
Scandals lead to firings like Kevin Spacey from House of Card