Bale just said recently that he and Nolan were both done after this film. I'd be surprised if an offer of money from WB was enough to get either of them to change their minds. If the stuff you read about Bale is true, he doesn't seem like the kind of guy that changes just because money is waved at him. If he doesn't want to do more films he won't.
But, of course, WB is going to do more Batman movies. So I'm assuming they'll just reboot and we'll get another Joker film sometime around 2015, 2016...
E...