I was thinking about this piece from Batman: The Dark Knight Returns. Batman retires for a decade or so and the Joker, not knowing what to do with himself, does nothing. He becomes nearly catatonic until (as you guessed from the title) Batman comes back.
I thought: "What would happen if the Joker killed Batman?"
Of course, he'd immediately regret it. Batman can exist without the Joker, but the Joker is nothing without the Batman. Eventually, I think he'd come up with a solution.
|The Bat Joke!|
What if Doc Ock decided to really punish Spider Man by forcing him to live with the horror that he has to deal with every day (permanent extra robot arms)?