That, Spike, is the big question right now. I have to assume there's a way to undo the seance, but unfortunately I don't know what it is... but don't worry! Remember, there are experts here, including a ghost type gym leader. If anyone can figure out how to deal with long-dead Pokemon, it would have to be someone like that.

[Actually it's Sabrina who's going to eventually figure out how to undo it, but Twilight couldn't know that and besides, Morty probably helped.]