“The Many Loves of Dobie Gillis” has series star Dwayne Hickman, Sheila Kuehl, Tuesday Weld (17 episodes) and Warren Beatty (5 episodes). Dwayne’s older brother Darryl is also living and appeared in two episodes as Davey Gillis but left with Chuck Cunningham
On the original “Perry Mason” for awhile in the fifth season they tried introducing a young law clerk played by Carl Held (first as a defendant). Either as a possible replacement if Raymond Burr left or to draw younger viewers; in any case he was superfluous and left after nine episodes . He appeared on Star Trek TOS “Return of the Archons”, his late wife Sarah Marshall was on the episode “The Deadly Years”.
“Lost in Space” has a number of people alive. June Lockhart is 95, Mark Goddard, Marta Kristen, Billy Mumy, Angela Cartwright still with us.
I was surprised that Nehemiah Persoff was still alive at 101 and at he was only on “The Untouchables” four times as Jake “Greasy Thumb” Guzik. For a show with a lot of cigarette smoking those actors seem to have lived long lives where as on “Dragnet” they tend to die in their late 50s or early 60s (Harry Morgan an exception).
As mentioned Nicholas Georgiade is alive at age 87. Great casting by Desilu…have a Greek (Georgiade) play an Italian-American and have an Italian (Paul Pucerni) play an Irish-American (Picerni played an Italian in the pilot and does speak it in the series, growing up in a mixed neighborhood of Irish and Italians).
Terry Carter, the original Colonel Tigh in “Battlestar Galactica”, is left from the “Phil Silvers/Sgt Bilko Show”. Not sure about others, Nat Hiken used a lot of people.