Kill Batman's Joker forever?

A group of Heath Ledger fans are demanding that the Joker character be forever retired from the Batman series in respect to Heath Ledger.

My first thought was, what a stupid idea.

Then I thought about how great Ledger was in the movie as the Joker and I kind of agree. OK. I don't agree, but sympathize. 

Certainly, I don't think Batman should again include the Joker any time soon. In the future, however, I think it should be fair game.

Why not?

Jack Nicholson was a great joker, but Ledger took the role to a higher level. He set the bar much higher. That doesn't mean another couldn't take it even higher, with Ledger as his influence. 

We should embrace Ledger's role, but Batman and the Joker should not define Ledger.

At least that's my take? What do you think?