I missed it. *minor spoiler ahead*
I did find the body of Ra's al Ghul in Batman: Arkham Asylum, but I didn't notice that it had later disappeared.
If you can fill your game with secrets, do it. Make some easy to find, and others near-impossible. Secrets get players talking about the game. The more secrets and the better they're hidden, the more talk there will be and the longer it will last.
Secrets can be a great marketing tool.