Anyhow, contrary to what Sprry said, there's always a possibility!! What others have done has no consequences! She is not an author in the traditional sense. I doubt she cares what others have done, she's only doing what's right for her characters! Since both his parents, Sirius, and Dumbledore are dead, it might be best for him to be at peace and join them! Sure he would leave behind Hermione and Ron, but them being together finally could comfort each other!
Again this is just an idea, a possible scenario. What would be stupid is too shoot others ideas down, just because you don't agree with them, that's stupid!