If I remember correctly from a documantary I saw once (I think it was called Color Pattern) they decided to kill off the father character on “Good Times” because they didn’t think having the father around was realistic enough. You know, because NO ghetto families have a father who sticks around.
Mutant X that wonderfully horrid syndicated show went for I think two more seasons after the main character Adam (the Prodessor X character) left.
Here in the UK, a long time ago, there was a cheap schlocky sci-fi series called Blake’s Seven. By the end of the series there were only six of them, and none of them were called Blake. At least, that’s what I’m told by aficionados of the series (not being much interested myself).
Yeah, that’s what I thought of when I saw this thread. Every single cast member from the first episode was gone by the time the last episode aired, including the puppet voices.
I was under the impression that John Amos left the show because he didn’t like the fact that Jimmie Walker was becoming the featured actor in the cast.
I just thought of another one: “Peyton Place.” I wasn’t even born when the show aired. But Mia Farrow was THE star of the show for about a year and a half, then famously eloped with Frank Sinatra and was abruptly written out. Mia later confessed in interviews she never thought the series would take off and hence didn’t actually expect to be tied down with a a contract to do the series for ‘x’ number of years. Sinatra used his clout to get the producers to let her out of the show, even though she was the principal attraction. (Imagine if, for a comparitive example, Sarah Michelle Gellar abruptly left “Buffy the Vampire Slayer” after only one season and her role wasn’t recast.) Nevertheless, the series went on for a good five years after she left.
Sooner than that. Episode #814 was the last time Jim Mallon did Gypsy’s voice. Episode #815 was the first show not to feature any of the cast from the first season.
General rule of thumb: shows set in a workplace (ER, Barney Miller, MASH, Mary Tyler Moore) can weather a major castmember leaving much better than shows set in a family (All in the Family, 8 Simple Rules, etc.). There are a thousand reasons people leave workplaces but very few that they leave families (divorce and death being the most common and those are just a tad too heavy for most primetime shows to deal with).
How about My Three Sons? By the end of its run, not only was it down to one son (plus a couple of orphans picked up along the way) but Steve Douglas also managed to off…sorry, grieve for Grampa Bud and then replace him with the creepy “Uncle Charlie”, plus move from suburban Chicago to Hollywood.
And what exactly happened to Mrs. Douglas, anyway? :dubious:
I think if one dug up the garden in the backyard of the Douglas home, one might find an old “ham bone” or two, if you catch my drift.
“Must have splattered a lot.”
Stranger
Power Rangers had several changes of cast.
Two more:
Bewitched survived the change of actors playing Darren…from Dick York to Dick Sargeant;
and Happy Days survived the loss of oldest brother Chuck. Who really got lost apparently…whaat??? 
Also two Public Defenders (the black woman (Liz?) and Billie Young) before Christine Sullivan, and a court clerk (Lena? Lana?) before Mac.
Paula Kelly was Liz in season one. Ellen Foley was Billie in season two. Markie Post assumed the role from season three to the end.
Karen Austin was Lana in season one. Charles Robinson would take over from season two to the end.
Trivia: in the unaired pilot (which, unfortunately, does not appear on the upcoming DVD set) featured Shelley Hack as the public defender.
According to TV Tome the public defender in the pilot was played by Gail Strickland, however this was aired. Was there an earlier one with Shelly Hack. The reason I’m asking is because I remeber that episode and Ms. Strickland did look a bit like Ms. Hack.
Actually, it would be harder to find shows that last for a while that didn’t have a major character leave. I remember the hubbub around the fact that Friends lasted 10 years without a major cast change. The odd thing was that nobody mentioned the fact that Frasier managed to do it for 11 years.
Sadly, there is absolutely no possibility that Mike (a/k/a John Morgan) will ever come back. 
“The Facts of Life” and “Roseanne” also survived the loss of George Clooney.