Hi Adslahnit mate! 
I think the only balanced way of doing this is really to have the revived immortal drop a permanent divine status (with appropriate loss of divine abilities* and ability scores from the template) but possibly keeping their class levels and Hit dice as before.
*potentially even losing this ability.

I think the only balanced way of doing this is really to have the revived immortal drop a permanent divine status (with appropriate loss of divine abilities* and ability scores from the template) but possibly keeping their class levels and Hit dice as before.
*potentially even losing this ability.