If the subject is a public figure and the play is not claiming to be a true biography, I think you are free to create a persona in a play about them. I am thinking about "King George 3", the satire on the very much living British royal family or "The Crown", TV series. And I'm sure no one had to get a waiver from Roy Cohn's family members when "Angels in America", with Cohn as a villain, was written and produced on Broadway. I recently saw a play about Robert Moses and I believe the playwright had to have permission from Moses' biographer Robert Caro but I doubt from descendants. There have been several movies about the Clintons and the Bushes, who are very much alive. And Madoff and his family. "Saturday Night Live" sends up many famous celebrities. There have been recent movies, not satires, about Princess Diana and Jackie Onassis, and a new one will be released starring Angelina Jolie as Maria Callas. I doubt their families were included in discussions while the screenplays were being written. That said, the families of Elvis Presley and Leonard Bernstein seem to have given their blessings to recent biopics. I personally don't have any experience with rights, but I do follow the entertainment scene.