I recall when Roger Davis replaced Pete Duel (who died of a self-inflicted gunshot wound) in the TV series, Alias Smith and Jones.
It just was not the same.
The series continued for another 17 episodes but never regained its popularity and was cancelled at the end of a shortened 3rd season.
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And there was the demise of the main character in Valerie Hogan [played by Valerie Harper who was fired at the end of the 2nd season]. The sitcom continued with Sandy Duncan but under the title Valerie’s Family and then The Hogan Family which ran for several seasons.
I think the ‘Save Baby Mark (S04 Ep05] is one of the most hysterical classics in sitcom history.
It is posted online at:
http://www.dailymotion.com/video/x54xvee