The theories here are getting weirder and weirder.
Soul being absorbed by the river sounds very much like the ‘Gia’ stuff in that Final Fantasy CG Film. Well, if there are souls in the river couldn’t mage/wizard/demon sight see them? Wizards seems to be able to see souls. Also shouldn’t mana be still attached to the soul or something?
Never heard of soul meld spell. Wonder if necromancers of Astlan could do it. Still quite impractical a spell if you ask me.