The fact that Rowlings gives Harry an opt out clause is a disappointing commentary on the book’s commercialism. I think that Rowlings meant to make Harry a martyr but her publishers made her go with the commercially correct ending that appealed to the teenyboopers instead...
I think Rowling ended the book in exactly the way she intended. It was a series intended for children after all, and a happy ending was completely appropriate for that audience.
This is the exact argument that fans have had for decades about Heinlein’s “Podkayne of Mars” where he wanted to kill her off at the end but the publishers wouldn’t let him. They were right, and you know why? Halfway through that story, Podkayne needs comforting and talks to her uncle, and he retells her favorite story from childhood, about little Podkayne and how the world was new and she swam in the canals and stared at the sky. And the real Podkayne told him to stop, he wasn’t making her feel better, but he continued with the part of the story she had always fallen asleep for:
“And then Podkayne grew up and had another little Podkayne. And the world was new again”.
That’s the kind of book Heinlein wrote without realizing it. That’s the kind of book Rowling wrote too. Sometimes it takes death to make the world new again. But sometimes it takes life, and she knows that.