I mean it is HEAVILY implied that Withers is the God Jergal, or at least a Avatar of him, so becoming his Champion should give you some sort of boon. In the lore even, Bhaal, bane and Myrkul became Gods by tricking Jergal with a deal, and gaining his powers, so wouldn't Jergal be able to bestow you some form or something?
He's the Scribe of the Dead and he already gives Durge his most powerful boon, a life independent of Bhaal and coming back to life.
