The effect of energy feeding would just leave her exhausted. He could drink her blood, in which case she would die. I don't know if Vampirization should come into play. Might make things complicated.
Since he can manipulate energy, feeding off of energy does give him more stamina, and more to work with when he uses energy to create anything, like force fields or energy swords.
I'm also thinking his medallion can trap souls, but I haven't decided if he can rip a soul out of a person's body, or if he has to kill someone, wait for the soul to come out, then trap it.
I think it would have more of an effect on Efaen than Terenia.