The fate of Sigourney Weaver's character, Grace, in the original Avatar seemed to have been pretty clearly shown on-screen, but Weaver's holding out for something more in the sequel. Spoilers, in case you somehow haven't seen Avatar yet.
Talking to Entertainment Weekly, Weaver responded to the idea that Grace was killed during the movie by saying,
Well, I wouldn’t use that word. I wouldn’t use that word — she was changed. You know, it’s science fiction, so we saw something happen to her, and we don’t quite know what it is. She definitely went into the Tree of Souls, right? It’s science fiction. What looks like death, who knows?
She went on to say that Ghostbusters III was most likely happening and that Bill Murray is on board.