McLeaned: Jean Stapleton left the series after the first season due to feeling the character had gone as far as it could go. This lead to Edith dying off-camera between seasons and was the premise for "Archie Alone". Unlike most examples of this trope, Norman Lear actually did this to give Edith a dignified end and apparently took the death of the character personally.
What Could Have Been: According to the 2001 E! True Hollywood Story special, if the show had continued, Mike would have returned for a cameo, and the show likely would have had (according to Carroll O'Connor) a proper series finale.