Of the 37 guest stars to be credited as special guest villain or villainess there were 3 that started with the letter J:

John Astin
Joan Collins
Julie Newmar

These are the only guest stars that are still living. Jill St. John is also still alive, but she was only credited as Molly and not as a guest villainess. If not for that technicality I would include her also.

We've lost so many of those actors. I might mention that one of the main villains from the 1966 theatrical film of Batman is still living: Catwoman as played by Lee Meriwether, but she played her in the film only -- not on the TV series.