I don't know happens in 5th either. In 2nd you would be destroyed -- you don't actually have a soul, just the tainted shadow of one and the taint would return to the negative material plane (or become a vampric mist under certain conditions). In 3rd you would be claimed by Orcus or Vesharoon but I dunno if anyone has decided with 5th.
5th has lots of "legends differ" descriptions so my guess would be that its another "up to the DM" decision.
I think it was the same in 3e, being undead was the same as having your corpse desecrated, so you had to do more than just resurrect them. I get the impression that the FR cosmology wasn't interested in asking or answering these questions.
