Didn?t read ?bout them quite for a time because I?m concentrating on Jaiman but such a nice cult!!
In the old Emer book it?s only written about the evil god Zanar. In Powers Terry changes it in this way, that the god Zanar war the official religion of the Aldarian Empire. And ?bout that because their was not such a god somebody else did "the mantle of Zanar" in this case Eissa. Later on Onodoval refocused the religion on the Jewel of Ahrenthrok.
The second part with the Jewel is thrilling, the first part completly boring. Again a God of Orhan "pretending" to be another god...yaawn!
Even if you go on with Terrys interpretation, think about if their can?t be a real god, Zanar, perhabs from Kulthea, perhabs (like the Aldarians) from another world? And I would make my mind up what chances this guy would have to come back to power? Can he come in dreams to one of your characters? Trying him to redirect your group to an ancient tempel of the original Zanar religion? If Eissa has put on the mantle of Zanar, Zanar was probably a local god of Earth in Emer. Now the power is redirected from Eissa again to the Earth, to the Jerak Ahrenreth Crystal. Could this place your characters in a religios war, trying to establish again the benevolent Church of Zanar against the existing Church of Zanar and Eissa??