Alive: Vin Scully, host of the original It Takes Two (I'd ask him, among other things, if he knows the whereabouts of any tapes of this show and his self-titled CBS talk show from early 1973), and Phyllis Newman.
Deceased: Art James (probably) and Carol Wayne (definitely, although I might not be with both at the same time, for as the title of that Chuck Barris game suggests, "Three's A Crowd") ; )