How do you know that JKR wanted Harry to die, and STAY dead? Maybe she envisioned this ending all along.
However, I guess that your right. Rowlings could have wanted this ending. But I don’t think that speaks highly of her as an author then. Instead of challenging her audience, she pandered to them on the lowest common denominator and gave them exactly the Disney teen ending they wanted.
She is said to have written that last chapter/epilogue before she wrote the books themselves.