I think Peter Falk should continue to make Columbos until he decides he's no longer up to the task. I agree with the consensus that the earlier episodes are superior to what's been served up since he "returned," but isn't that true of nearly any endeavor in the arts, sports, etc. I don't play chess as well as I used to when I was younger--but I can still provide enjoyment for myself and others when I do play. Even though Lance Armstrong may slow down, I'd never advise him to quit--he's made that decision by himself. And he's still the champ, just like Peter Falk/Columbo.
I think it would be great to see an episode which had some of the old crew from the original 45. Producers, writers, directors, editors and even some of the actors who were semi-regulars. Maybe they could capture some of the old magic.
They should do 1 more and end it all in a very good way using some of the older cast from the 70's. I like the idea of an original 70's murderer making a comeback. Also Columbo likes the nightlife would be an unsatisfactory way to end it all - really push the boat out.
Hopefully the reality faze is over as i didnt like that idea at all.
If they were to do only one more episode then it should have a finality to it. I think when the episode ends Columbo should retire, whether we know it from the beginng (wouldn't that be ironic) or it is a surprise to us all at the end.