Opposite of breakout characters on hit TV Shows

[roadman65]

The Facts of Life gave all the girls Chuck Cunningham Syndrome.  At the start of Season 2 they had the four girls get into mischief which caused them to be moved out of the girl's dorm and move into a spare room over the cafeteria where they had to work off the damages to the school van they destroyed.  Mrs. Garret received a promotion coincidentally at the same time where she became the school dietician.

Therefore the girls who did not get to stay really were staying as the show moved out of the dorm, so the others (including Molly) lived on in the dorm but no coverage.

As far as Mr. Bradley went, he was just not there with no mention (many shows do not write out characters so this is not new) of if he quit or got fired or even moved.   Jenny O Hara, also appeared in the first three episodes as a teacher of that school, but also just vanished as well.

The Doris Day show in the early 70's had more supporting actors disappear than anything as each season of the show was self contained where no stories carried over the summer break.  In fact in the final season, Doris Day became a single never been married 70's lib woman as in the previous seasons she was a widowed mom with two sons.   Actors like McClean Stevenson, and Rose Marie had good supporting characters, but never returned after their one season on the program.

What about Cody Lambert on Step By Step?  He vanished in one season as he was a key supporter of both Patrick Duffy and Suzanne Sommers characters also added to the cast after the fifth episode as he was intended only as a guest star, but was well received by the audience.  He really did break out as a character not being original to the show, but dropped later on.  Sasha Mitchell (who was also with Patrick Duffy during the last two seasons of Dallas) was his name, and most likely came on board at the request of Duffy after just starting his role on this show right after Dallas was cancelled decided to cast Mitchell.

Linda Gray's character on Dallas too was cast aside at the end of the second to final season as well due to her Sue Ellen character being fully developed that producers felt there was no more room for it anymore. 

Lenny on Laverne and Shirley too was one that made fewer appearances in the end run of Laverne and Shirley.  Toward the end right after both Michael McKean and David Lander received front billing in the opening sequence both characters appeared less and less, however Squiggy was in a few final season episodes. I believe that McKean was involved with other projects as in addition to being an actor and screenwriter, he was a director and started pursuing his career in films and therefore not acting on L & S.   

[vdeane]

Boston Legal regularly shed a few characters between seasons (and sometimes in the middle of a season).  Usually they were more minor characters, but in Season 4 Paul Lewiston was promoted in universe (so in actually demoted to recurring), and he was to that point a very major character who was there since the show began.  Season 3 also had an odd situation where a main character introduced that season was written out, only for a couple recurring characters (both introduced in that season) to join the main cast later in the season, one of whom did not return for Season 4.  Sometimes they had reasons for leaving, but often they vanished without a trace.  One even vanished without a trace only to show up out of the blue in one episode in a later season working for another firm.

[roadman65]

Valerie Hogan was a character that was popular (the show was even named after her) until in real life Valerie Harper had it at with show's producer over salary which led the top brass to fire her and write her character off the show.

Thus Sandy Duncan took her place, still her role as lead was not as front and center as Ms. Harper's was.  During the seasons with Duncan as the star, Jason Bateman started to become more in the spotlight and so were the other two actors which made the show's main focus about the 3 Hogan boys rather than the mother figure trying to come up with the solution as Valerie had done in the first season.

Also Edna Garret on the Facts of Life as in the final seasons of the show was not there.  Charlotte Rae quit the show, so her character was no longer a main feature of the show. Though Cloris Leachman filled her role, Leachman really played a supporting role as pretty much the story lines focused around the lives of the four girls.  Beverly Ann Sickle ( Edna's Sister) was there to run the business, but was there mainly to be a friend and mentor to the girls who then pretty much solved their own problems.