Long after a pony's mortal form has passed away, their soul persists in the Ethereal Realm. Those who are judged to have lived a worthy life may ascend unto Heaven, and evildoers will pass into Hell for all eternity. Nopony knows what sort of actions end up with your soul powering Twilight Sparkle's coffee maker but, given that an eternal soul is an eternal source of energy, Twilight isn't complaining.
Written in response to a blog which calculated the inflation-adjusted value of a human soul based on the song, 'The Devil Went Down to Georgia'.