I don't think that what Molly or Hannah did is really relevant to killing a shapeshifted human who is under the influence of the Wild Hunt, since in Molly's case it wasn't killing, and in Hannah's case her victims weren't shapeshifted.
I maintain that the closest comparison to what the Wild Hunt does to humans (if it doesn't kill them) would be a werewolf curse, and that killing someone who is in the Wild Hunt would have similar effects on the killer to killing a werewolf.
And Harry had already gotten away with killing a werewolf.