Most TV actors who get a featured part in a series (even a hit series) vanish. Those who don't are the exception, not the rule. Very, very few go onto to movie careers (Clint Eastwood, Tom Hanks, and others). Very, very few get a second hit series (Mary Tyler Moore, Bob Newhart, Ron Howard, Bea Arthur, etc - even the aforementioned Guy Williams). Very, very few keep popping up again and again (Betty White, Shelley Fabares). At one time time, there were shows that seemed to go out of their way to keep former TV stars from disappearing all together by supplying guest roles for them (The Love Boat, Fantasy Island, Murder She Wrote) but those shows with old stars generally attracted an audience of old demos, so they aren't around much any more.
Smart actors know the one show may be it and they carefully invest their earnings and don't need to work again.
Some, like a lot of people who start out in broadcasting, know show biz is not a safe or stable career path and go do something else.
Some hang on and end up doing dinner theater in small towns.
Some have integrity and want to be real actors and return to the stage.
Some end up on soaps.
But the person I miss the most is the sweetheart of radio geeks everywhere: Jan Smithers (Bailey Quarters of WKRP in Cincinnati).
