I know you folks like a challenge, so I figured I'd crowdsource this one on account of Paizo not having rules to cover it.
A little background: my pet project is a campaign setting where Nethys...dies/is killed. And they take with them the ability to craft new magic items, access to mythic power for mortals, and most importantly all spellcasting for full casting classes. Arcanists, Clerics, Druids, Oracles, Shaman, Sorcerers, Witches, and Wizards all completely lose their ability to cast spells. They keep their other class features, like witch hexes and the cleric's channel energy and domain powers, but no casting (the clergy of Nethys gets it worse; they all either die or lose their minds from divine backlash).
My query, then, is this: I am designing a nosferatu villain to be one of the BBEGs for a campaign. He is a follower of the Horseman of Pestilence, and was a cleric and souleater before the Fall. So when the PCs meet him, they face a villain with no spellcasting but with his domains, channel energy, and supernatural powers from the Souleater prestige class intact. I'm thinking of pegging him at (human?) Nosferatu Fallen Cleric 5/Souleater 10 (or thereabouts), but his CR can't be 16- it simply wouldn't make sense without his spellcasting, upon which the Souleater class builds very heavily. So, what do you think?
Other suggestions on how to optimize him in the face of this are welcome, of course, but he'll have at least two wasted feats (probably Combat Casting and Empower Spell) that were, when he took them, perfectly valid.