Poor Sybill Trelawney.* First Umbridge has at her in Harry Potter and the Order of the Phoenix, in front of all the students, no less. Now she's really been sacked! At least, she has been from the next movie. After hearing that Moaning Myrtle was left out of Harry Potter and the Half-Blood Prince, Snitch Seeker reports that so is Emma Thompson's Trelawney. A Hamilton Hodell rep said: "She is not in the Half-Blood Prince."
As the site points out, this means that she won't be able to play helpful informant to Harry. (What she tells him, I'll leave out to save the eyes of those who haven't read the books yet.) With two important players out of the film, it begs the question of how the story will come together. I imagine their important roles in this part of the story will be given to another character, but who? We'll have to wait until November 21 to find out.
*The UK/Canada spelling is being used. I've no idea why it's spelled "Sibyll" for the US.