Lena Headey does such a wonderful job of playing Cersei Lannister on Game of Thrones that even fans who hate her character can't help but admire her. However, there are a lot of rumors floating around about Cersei's possible death in Season 5, even though Lena's done nothing to suggest that as a possibility.
That being said, book readers are well aware of what happens to Cersei's character in the books, at least until A Dance with Dragons, which was the most recent release. According to the books, Cersei becomes the Queen Regent again, following Tywin Lannister's death and the dissolution of her marriage to Loras Tyrell. She manages to use her power to get rid of Tommen's engagement to Margaery Tyrell, and then uses that to accuse Margaery of infidelity.
However, her own rash decisiont to empower the militant-based Faith of the Seven backfires on her, as the high militant of the Faith decides to turn the tables and accuses Cersei of infidelity. In fact, Cersei is accused of many things including infidelity and incest, and it eventually comes to a place where she loses all power and is forced to undergo a trial. During the trial, she has to shave her head and strip naked, and then proceed to walk through the streets of King's Landing. While her story ends there, it's likely that the show won't reach that point until Season 6, so we still have two more season of Cersei's scheming to get to before we can even entertain the notion that she'll meet her untimely end in Season 7.
There's also the possibility that the showrunners decide to follow a completely different plot than the books, and keep Cersei in control and ruling for longer than the books. But considering that Cersei's fall from grace is such a major change in the story, we're guessing that they won't deviate too far from the books.