Complex sentence: Finger wanted the Joker to die because of his concern that recurring villains would make Batman appear inept, but was overruled by then-editor Whitney Ellsworth; a hastily-drawn panel, indicating that he was still alive, was added to the comic.
Split into simpler sentences: Finger wanted the Joker to die, as he was concerned that allowing recurring villains would make Batman appear inept, but he was overruled by then-editor Whitney Ellsworth who suggested that the character be spared. A hastily-drawn panel, demonstrating that the Joker was still alive, was subsequently added to the comic.