Does Nassan Falls have a mortal equivalent - and does the soul reach Nassan Falls prior to the underworld? Dinn is conveniently the patron of running water, so it wouldn't be much of a stretch to adapt that into the current set-up.

Incidentally, is it legit that a soul not divorced from its body 'degrades'?

Edit: also, if the life cycle is indeed a cycle, would it therefore be reasonable for Dinn to preside (even if incredibly passively) over the return of souls to the mortal plane, or would that make his portfolio a little too ginormous?