Questions on latest episode.
[spoiler]When Katherine took over Elena, it was very important to her and Nadia to get rid of the body so that Elena couldn't reassert herself, as she did a few times.  Supposedly that would completely end Elena.  I assumed they would find a way around that to bring her back, but there was no explanation of it or even showing her come back.  Suddenly she's just there again.[/spoiler]