It's a joke he's making from a line Venkeman said in Ghostbusters 2. How do you know IDW didn't have much of a choice when he was killed off? For all we know Hasbro might have told them to kill him off. Also they could have tried to call him Sling at least but weren't able to. From what I've heard trying to reclaim or trying to make up for lost copyrighted names aren't easy at all.