The nutcase that left Bonanza because he was afraid of being typecast , Pernell Roberts. Didn’t see much of him afterward.
Trapper John MD.
Then you have guys like James Arness who rode Gunsmoke right into old age and then made a couple of Gunsmoke movies.
He went on to do Trapper John MD which had a good run for 7 years.
According to wiki, he had guest appearences in 60 different shows.
I was just a kid when that happened but I get the impression that a lot of viewers really resented it when he left. People loved their Bonanza and they didn’t like it when big shot actors messed with it.
Pernell Roberts had a decent run on “Trapper John, MD”, based on an older current day version of Wayne Rogers character.