Producers would surely have feared losing their audience
One serious sad episode about Mr. Wilson dying might have led to the show's cancellation. Forget about whether we today think it should have ended when he died. The people working on the series--all the crew, cast, and executives had plenty of reasons to want the series to continue.
I doubt anyone connected with Kearns or the series at that time thought they were doing anything the least bit insulting to him.
what was the circumstances in introducing Gale Gordon as Mr. Wilson's brother? And what happened to Martha Wilson?
I don't think TV ever made mention of an actor when they died like they do now.
Only with the rise of entertainment journalism did the need arise to mention an actors death.