According to Clint Morris at Moviehole.net:
Katie will indeed be reprising her role as Rachel Dawes for the “Batman” sequel – as brief as her turn may be. Can’t say anymore without being pummelled by David S. Goyer.
Nice. I have doubts whether we’ll be fortunate enough to see a grisly on-screen death for Kirsten Dunst in Spider-Man 3 (you’d think the least Harry Osborne could do would be to accidentally kill her and blame Spidey for it) but the next best thing is to see Katie Holmes bite the big one, probably courtesy of the Joker. All in order to provide Bruce with some additional motivation, of course, and give him an opportunity to kill the Joker, then decide not to indulge his vengeance.
In general, I’m a fan of characters returning even if it’s just to be killed off (Cyclops) rather than just being ignored (Nightcrawler). HT: Cinematical.