Parts of the song can be heard in "The End", but it cannot be identified as a variation of "Parting Words" from the episode, as the tunes differ slightly.
Daniel Widmore and Drive Shaft play a rock/classical fusion song during the concert. Charlie stops playing when he catches sight of Claire.
Later on, Eloise sits by Desmond. She scolds him for his mission, but he refuses to accept her criticism. She finally asks whether he plans to take her son with him when he's ready to move on. Desmond says he won't.
The entire piece is a rock/piano variation of "Parting Words". Like several variations, it uses some rhythms from "The Gathering".