I believe elves had to adapt to life without a soul in which case, the soul is just a link to your god. The problem is that if you remove it, as it is a vital part for non-elves, one dies(the necromancy spell keeps it in a rock but is probably still "linked" to the body). It is like removing the spine of a vertibre(s.p.). The creature will die, but there are creatures who have adapted to life with out a spine.