Info derived from the imdb; credits not yet complete. Only actors confirmed in 2+ episodes noted. As Self if not otherwise noted. Only works 2013 and later being tracked.
Robert Keeshan (Captain Kangaroo): died in 2004.
James E. Wall (Mr. Baxter): died in 1981.
Hugh Brannum (Mr. Green Jeans): died in 1987.
Deborah Weems (Debbie/Phoebe/Baby Duck): died in 1978.
Alan Arkin: in Love the Coopers (2015), BoJack Horseman (3 episodes 2015), Million Dollar Arm (2014), Grudge Match (2013), In Security (2013), The Incredible Burt Wonderstone (2013); Going in Style (2016) completed; as Self: Alan Arkin: Live from the TCM Classic Film Festival (2015), Kevin Hart Unedited (2014), In the Ring with Kevin Hart (2014), The Bull & the Stallion (2014), Inside Comedy (1 episode 2014), MSN Exclusives (unknown episodes 2013), The View (1 episode 2013), The Lowdown on Making Stand Up Guys (2013), Stand Up Guys: American Muscle - The Stand Up Stunt Driving Scenes (2013), Stand Up Guys: The Stand Up Songs of Jon Bon Jovi (2013), The Oscars (2013), 19th Annual Screen Actors Guild Awards (2013), 70th Golden Globe Awards (2013); as Self, post-production: Sills (2014).
Shari Lewis: died in 1998.
Dick Shawn (Doc Grannick the Mechanic): died in 1987.
Ann Leonardo: no known subsequent acting roles.
George Zima: no known subsequent acting roles.
Stu Kerr: died in 1994.
Lorne Greene: died in 1987.
Kevin Clash (Kevin): in Sesame Street: Elmo: The Musical 2 (2015), Sesame Street (7 episodes 2013-2014), Sesame Street: Fairy Tale Fun! (2013; also Producer/Director), Little Children, Big Challenges (1 episode 2013), Plaza Sésamo (1 episode 2013); as Director: Sesame Street: Alphabet Songs (2014), Math Bites (5 episodes 2014), Sesame Street: Being Brave (2013), Sesame Street: Elmo the Musical (2013); as Self: Katie (1 episode 2014), Turtle Power: The Definitive History of the Teenage Mutant Ninja Turtles (2014).
Irving Harmon: no known subsequent acting roles.
Cosmo Allegretti (Dennis the Handyman / Mr. Moose / Mr. Bunny Rabbit / Grandfather Clock / Miss Frog / Mr. Whispers / Word Bird / Dancing Bear): died in 2013.
Lu Ann Simms: died in 2003.
Gwen Verdon: died in 2000.
Kira Willoughby: last known acting role in 1989 but Tar Beach (nd; also Casting Director/Producer/Writer) in pre-production; as Production Coordinator/Co-Producer: Can I Get a Witness Protection? (2016); as Production Coordinator, pre-production : The Peculiar Perils of Penelope Peacock (nd); as Casting Director, pre-production: Ryann Watters and the King's Sword (nd); as Co-Producer: 8-Bit Animal Playhouse with Jason Mewes (unknown episodes 2013); as Co-Producer, post-production: The Burning of Wildgoose Lodge (2016); as Producer, pre-production: Awakening (2016), Miracle Falls (2016); as Producer, in production: Justice Angel (nd); as Casting, pre-production: Here Without You (nd); as Production Coordinator, Los Angeles Unit: The Martial Arts Kid (2015).
John Burstein (Slim Goodbody): last known acting role in 1995.
Terry Kelly (Orville the Dragon): no other known acting roles.