It all started after being foiled with getting rid of Krusty for mistreating Sideshow Bob by framing him for armed robbery, afterwards he would make recurring appearances throughout the series for evil schemes that do and don't involve Bart. One of these years we will be due for seeing the last of it, whether it be from the show finally coming to a finish or from something that happens to Sideshow Bob's voice actor Kelsey Grammer. How this sendoff could happen meanwhile is Sideshow Bob officially putting an end to his villainy, or he maybe he'll actually killed off in some form like perhaps being sent to the Electric Chair.