They decided not to renew their contract for season 7. Chad Michael Murray said that he wasn't being brought back for season 6 because they wanted to save money. Hilarie Burton said that the she had a great time on the show and she mentioned that it wasn't about the money as to why she is leaving. She posted a video where she mentioned that she wished she had creative control over what was going on.
Chad and Hilarie are not a couple as Hilarie Burton is married to Ian Prange, an assistant director, but in the show Lucas and Peyton had a happy ending where they drove off into the sunset (leaving Tree Hill) with their daughter, Sawyer.
