In some many cases, some actors/actress leaving a popular television series that were mostly associated with for many years, some folks say "This show is not the same without (him/her)" or went downhill or in the JTS world they call it "Exit...Stage Left". Here's my examples of stars leaving their shows:
Miriam McDonald: Degrassi: The Next Generation as Emma Nelson from 2001-2010 and her final episode when she married Spinner (Shane Kippel) at a beach wedding.
Kathryn Leigh Scott: Dark Shadows in September 1970 after playing various roles (including Maggie Evans) from 1966-1970.
Steve Carell: The Office (US) as Michael Scott from 2005-2011.
Trevor Bannister: Are You Being Served? as Mr. Lucas from 1972-1979. He died from a heart attack last year
John Cleese: Monty Python's Flying Circus after 1973.
Demi Lovato: Sonny with a Chance from 2009-2010. She left because of a heath scare and went into rehab. Rechristened as So Random! in the summer of 2011.
Miriam McDonald: Degrassi: The Next Generation as Emma Nelson from 2001-2010 and her final episode when she married Spinner (Shane Kippel) at a beach wedding.
Kathryn Leigh Scott: Dark Shadows in September 1970 after playing various roles (including Maggie Evans) from 1966-1970.
Steve Carell: The Office (US) as Michael Scott from 2005-2011.
Trevor Bannister: Are You Being Served? as Mr. Lucas from 1972-1979. He died from a heart attack last year
John Cleese: Monty Python's Flying Circus after 1973.
Demi Lovato: Sonny with a Chance from 2009-2010. She left because of a heath scare and went into rehab. Rechristened as So Random! in the summer of 2011.