Along with Dr. Heideman, there's also Marsha in A Stitch In Crime. In their one scene together, she really seems crazy about Dr. Mayfield.

Nearly the most obvious one for me is Linda in The Most Dangerous Match. You see her in the background when Columbo first confronts Emmet in that crowd, but nothing more dramatic from then on.

Mr. Rowe (Justin's Dad) tops the list for me. I'd also like to see "the folks back in New York", in the Nightlife episode. Justin would have been taken care of faster than Lee Harvey Oswald was. I'd like to see Jessica Conroy's reaction if she were still wearing the bikini, lol. In "Old Fashioned Murder" I'd like to see Janie's reaction if she were intellectually capable of understanding what happened. I could see her ten years later, flicking a cigarette ash into a priceless heirloom when it finally dawns on her. Also Vincent Price would be interesting. With Vivica out of the way he could dominate the industry.

Interesting topic indeed, I agree rowe's father would be very interesting, agree about clifford making some joke, as for santini's daughter you can imagine sadness being the main reaction, judging by montoya's daughter's reaction, and fielding's daughter was already disappointed by her "father", imagine after finding out he murdered jerry, probably incredulous!