I don't know if this is unpopular, but I think Miko should let her father go.
It feels like it would be impossible for her to get over the loss of her father if he keeps existing in this ghost state between living and dead. I think letting the dead die and rest, where they have no duty to fulfill, may also be the best outcome. It's a bit like that monster in the hospital, the young boy, and the old lady, who rode off in the sky together.