But by then he won't be a child, he will be 17 or 18, (and most of her readers will probably be older still.)
It isn't a good ending, I agree, but the alternative would be for her to continue to write about his adult life for ever.
You can see people asking for more and more stories -- the same pressure Colin Dexter had over his 'Inspector Morse' novels, or that John Sullivan has had for his TV series 'Only Fools and Horses'. There is nothing new in that, Arthur Conan Doyle was also pressured into more 'Sherlocke Holmes' stories.
You can have too much of a good thing. The only way she can put Harry to rest for good is to kill him off.
But I would like to see how he turns out as an adult, with children of his own. Nic's idea would work, with a kind of epilogue taking everyones story to completion.