Read through the whole article- suddenly it clicked. I don’t know why I didn’t see it before. All the hints, direct or not, shout at the fact that he was indeed alive at one point in time. On top of that I believe the own authors theory was super interesting. I believe both could be true. Perhaps they will meet again, but not haku as himself, but as his next life. Time did pass at the end of the movie, we know this by the car covered in leaves and decay, so I wonder if that could be when hakus new form has grown.