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.