Let's say you had the power to get rid of any villain in comics, who would it be? For me it'd be the Joker. Here's the idea I have.
I'd build up a final confrontation with Batman, him and Jason. The big theme would be whether or not Joker should be killed after he does something big. Pretty much everyone in Gotham wants to kill him and it's pretty obvious that he'd get the death penalty only its doubtful if he'll make it that far. Jason wants to kill him and be done with it arguing that people are already working themselves into a frenzy to end the clowns' life. Bruce thinks he can just lock Joker up in some secret prison he can make and no one else likes that idea. Most of the family figure the Joker is a dead man. They either think he should just be brought to justice (which is made near impossible with so many gunning for him) or just let Jason follow through. Those hunting him down are getting more reckless and endangering innocent lives and the family can't be everywhere at once.
Bruce and Jason argue over this with Jason wanting to know why Bruce is willing to protect scum. The whole no kill rule would be explored but everyone Joker harmed would be upset with Batman. The final showdown happens with most of the family busy except Batman and Red Hood. Their with Joker. I'm not sure if I'd show Batman deciding to save Jason which results in Jokers' death or have an explosion with them escaping yet not saying what happened. We'd see Joker dead but their silence will make people wonder if Batman killed him.
Afterward either someone like TwoFace would rise to become his new archenemy or Harley would take over although she won't do overboard like Joker did. Jokers' legacy would remain strong in Gotham like with groups like the Jokerz.