Re: What if Columbo met a seventies murderer in a later episode?
If we consider villains played by actors who are still alive, Hector Elizondo could be a prime pick, given how international figures periodically reemerge on the world scene. First Secretary Salah could have been traded for an American hostage and climbed back to prominence under a new Surian regime.
Dexter and/or Norman Paris (Martin Landau) are charming sorts and could easily have finessed a parole board into early release. Perhaps they'd like to avenge both themselves and their old culinary school bud Paul Gerard.
Ah, and Honor Blackman is still with us. How about some Shakespearean-style revenge by Lilian Stanhope on behalf of the now-insane Nicholas Frame. There's the rub (that's about all the Shakespeare I know).