Hell no he shouldn't be retired. In fact he should be in the next movie too. I thought Ledger did a great job. He made the character real. Does that mean nobody could match or emulate him? No it doesn't. I'm a huge Joker fan and I don't want some actor who overdosed ruin the future of the character. Maybe that's not a fair statement. I look at it this way. He did a great job and the fact that someone would have to start by emulating him to keep the thing going would be more of an honor to him than retiring the character.