If you dont save him, the game ends and the credits roll. You then hear Oracle sending a transmission for however hears it saying how Joker killed everyone, that he had won and there is not a single person that can stop him...it ends with her asking for help.
Then the game rewinds and sends you back to choose the correct way XD --- Real Hulk: Gets stronger the more angry he gets. GameFAQs Hulk: Gets stronger the more angry his fanboys gets. And they are always super angry.
You can replay any catwoman chapter from the main menu you know. Her 3rd chapter isn't really all that long. --- A second ant? No, no, it's his brother, avenging the death of his twin. It's his twin brother! I'm going to follow him home...kill his whole family.~Space Ghost
As someone already stated, you can replay that missian whenever you want. Why watch aa YouTube video when you can see the credits yourself in 720p? ;-) --- "Are these guns firing or is someone cracking chestnuts?" 3.0 Sound
It's nothing special... you literally walk out a door into a stairwell and the credits roll (which they don't allow you to skip) --- "Ars Longa, Vita Brevis, Occasio Praeceps, Experimentum Periculosum, Iudicium Difficile." -Hippocrates