User blog comment:Mystery119/Marvin Monroe/@comment-85.247.233.108-20130802212746/@comment-108.213.151.111-20130819035232

Actually, Monroe was brought back later in the series. In the season 15 episode, Diatribe of a Mad Housewife, Marvin tells Marge that he loved her book. Marge tells him that she hasn't seen him in years and he tells her that he has been very sick.