"Meanwhile, the producers have confirmed that villainous housemaid Sarah O'Brien won't be back. Siobhan Finneran, who played her, is leaving the show."
As I understand it, actors in England commit to a 3 year contract. Mathew, Sybil and O'Brien actors did not want to sign a new contract or continue. Sybil and Mathew both died in the show. The article did not say how O'Brien is leaving.
Do you think she'll get hers before causing her to leave or that she is just written out? 11 months to find out.