Sigourney Weaver seems very sure she'll be in Avatar 2, despite the death of Grace Augustine at the end of the original film.
"Don’t worry, I will be back. [James Cameron] says no one ever dies in science fiction," Weaver explained in an interview with Coming Soon magazine.
"He’s told me the stories for the next two movies and I have to say that they’re absolutely wonderful and there’s a real treat in store. Now we just have to make them."
For his part, Avatar Director Cameron didn’t seem pleased with Weaver letting the cat out of the bag. In a separate interview with Vulture magazine, he almost seems to contradict her.
"Did I say she was going to be in Avatar 2? Well, I don’t want to disabuse her of that fantasy. But have you ever heard of nonlinear storytelling? A lot happens on that planet before she shows up, and before Jake shows up to join her. She’s there for fifteen years ahead of time. I don’t know, but I wouldn’t jump to conclusions.
"And I’ve already said way too much about Avatar 2 and 3 here and there, but people piece it together like those voice cameos and tell the whole story!…When you have a science-fiction series, a science-fiction franchise, you’re never dead, unless your DNA is expunged from the universe. And then there’s always time travel!"
It seems like Cameron is trying to say that Weaver won’t be in the films, but perhaps he’s only trying to say that the character won’t be ‘back’ in the sense she seems to imply. It could be that the character will be used without actually returning to the storyline - like through a series of flashbacks or recordings, or even that she’ll be represented somehow within the world as a spirit or some other non-human form based in the story universe’s functional magic.
As Cameron says, this is sci-fi, anything is possible, and resurection is a common element of the genres. It’s significant to note that one of the major themes of Avatar (in fact, the film is named after the technology that makes it possible) is that bodies are just bodies, and who we are transcends our physical form.
Sigourney Weaver herself is a perfect example of a returning actor if we look at how many times she’s been in an Alien film. I’m personally not yet convinced that her character in Avatar is not somehow the same person, or a daughter or grandmother or clone or something.
It was also established in the plot of Avatar that on this planet, living things do not die, they join their consciousness with the great glowing tree, so it’s entirely plausible that her ‘spirit’ is still hanging around, perhaps waiting for another avatar to inhabit, in which case, we’ll get weaver as a mo-cap actor only.
In the end the statement might just be misdirection from Cameron, who is usually pretty secretive about the plots of his films.
Avatar 2 is planned for a 2014 release.