The rules of this series tend to bend a lot, but no death of significant characters ever occur without turning into ghosts, and since they have two characters(Bonnie and Jeremy) who can see ghosts and haven't seen her yet. I'm sure Elena's more trapped in her own body than dead.
Either way, I believe her return in inevitable, in one form or another, unless the writers are ready to make history. No storylines of any fictions that ever involved possession or body swaps of main characters ever ended with the said main characters' bodies to be taken away for good. So she'll be back