At one point while talking with Harvey at the coffee house, 'Sabrina The Teenage Witch' says, "Turn the world on with my smile? Oh wait. That's Mary."
Of course we know that to be a lyric from the theme song for 'The Mary Tyler Moore Show', and that from our viewpoint, Sabrina is talking about Mary Richards.
But within the "reality" of Toobworld, it doesn't have to play out in the same way. Sabrina may have been referring to a girl named Mary that she and Harvey both know from school. As the audience viewing along at home, we're not always going to see every detail of these characters' lives - such as friends named Mary who can turn the world on with their smiles.
So, the Zonk is magically deleted!