The party is over, and all of Gotham is trying to figure out what they're going to do with a psychotic clown on the loose. At no point does anyone feel the need to discuss just what the fuck happened when Batman left a room full of Gotham's wealthiest citizens completely alone with the craziest motherfucker in town.
"Sometimes I hear oranges."
Keep in mind that before Batman arrived at the party, the Joker was literally about to cut someone's face open in order to find Harvey Dent. Yet, when Batman jumps out the window to save not-Katie Holmes, he never returns. The Joker is alone with a crowd of unarmed victims. And Batman just bounces?
Eh, they'll be OK. It's not like he's crazy enough to blow up a hospital or something.
OK, sure, Batman is right downstairs, so it's possible that perhaps the Joker got spooked and made a run for it. But even if he did ... well ... Batman is right downstairs. How in the hell did he even escape the situation? He's on the top of a skyscraper and Batman is the doorman. Did Batman get off that car they landed on and go get a burger or something?