Well, no matter what happens now in book 7, she can change it of she wants to, can’t she?

Rowling on 8th Potter Book: “Never Say Never”
Author J.K. Rowling has apparently left the door ajar for an eighth Harry Potter novel.
Asked during a BBC interview Friday night about the possibility of reviving the series in the future, Rowling reiterated that her seventh book, Harry Potter and the Deathly Hallows, to be published on July 21, will be the last, but she added that her motto has always been “never say never.”
A spokesman for Rowling said Sunday: “It’s not saying that she definitely is [going to write another Potter book], and it’s not saying that she definitely isn’t. I cannot comment further.”
Meanwhile, the British bookstore chain Waterstone’s launched an online petition Sunday that begins with the words, “We, the undersigned, petition J. K. Rowling to write more new adventures for Harry Potter and his friends no matter what happens at the end of Harry Potter and the Deathly Hallows.”
And what if Rowling kills off Harry in the final book?
Well, the bookstore observed, Sir Arthur Conan Doyle killed off Sherlock Holmes in 1893 in The Adventure of the Final Problem but brought him back to life after a public outcry.