Info derived from imdb. Only roles 2013 and later still being tracked. Only actors in 2+ episodes noted.
Jean Vander Pyl (Wilma Flintstone, Pebbles Flintstone): died in 1999.
Alan Reed (Fred Flintstone): died in 1977.
Mel Blanc (Barney Rubble, Dino): died in 1989.
Bea Benaderet (Betty Rubble): died in 1968.
Don Messick (Bamm-Bamm Rubble, Hoppy): died in 1997.
John Stephenson (Mr. Slate): died in 2015.
Gerry Johnson (Betty Rubble): died in 1990.
Hal Smith (various): died in 1994.
Doug Young (Grand Poobah, etc): last known acting role in 1988.
Howard Morris (various): died in 2005.
Daws Butler (Barney Rubble, etc): died in 1988.
Henry Corden (various): died in 2005.
Harvey Korman (The Great Gazoo): died in 2008.
Allan Melvin (various): died in 2008.
Jerry Mann (various): died in 1987.
Janet Waldo (various): last known voice acting role in 2000 video game, 1998 non-video game; as Self: I Know that Voice (2013).
Frank Nelson (Clerk): died in 1986.
June Foray (various): in Rocky and Bullwinkle (2014), Dustland (2013), DuckTales: Remastered (2013 video game), The Looney Tunes Show (3 episodes 2013); as Self: I Know that Voice (2013), The One and Only June Foray (2013), 2013 Primetime Creative Arts Emmy Awards (2013), VO Buzz Weekly (2 episodes 2013).
Paula Winslowe (various): died in 1996.
Verna Felton (Pearl Slaghoople): died in 1966.
Herschel Bernardi (various): died in 1986.
Howard McNear (Doctor): died in 1969.
Elliot Field (various): last known voice acting role in 1983.
Herb Vigran (Cop): died in 1986.
Nancy Wible (various): died in 2015.
Paul Frees (various): died in 1986.
Bob Hopkins (various): died in 1962.
Dick Beals (various): died in 2012.