I don't think reviving her would necessarily be an asspull. Hiyori is already an exceptional existence, being part living human, part ayakashi. Her death is equally exceptional: no damage to the body nor the spirit, just that the link between them was forcibly broken. Thus, this is a novel situation, where not even gods know how things can or should play out. It would not be unreasonable for there to be a method to repair the damage. Even in reality, there have been people who were "clinically dead", yet successfully revived. So who's to say that it is impossible for the link to be restored?
Of course, it's all predicated on good writing. Just because there can totally be a reasonable, believeable method of reviving Hiyori, doesn't mean the author will write one. I hope there will be one, because the existence of a living human-ayakashi-shinki hybrid sounds cool as fuck to me, but we'll just have to see.