Spellbook Seeker // Careful Study

A preparation card is a creature card in every zone. For example, while it's in your graveyard, Emeritus of Ideation is a blue creature whose mana value is 5. It can't be the target of Zealous Lorecaster's triggered ability ("When this creature enters, return target instant or sorcery card from your graveyard to your hand.").

If a prepare spell with one or more targets has no legal targets when it tries to resolve, it won't resolve and none of its effects will happen. Since the spell was cast, the associated permanent will still not be prepared.

If a prepared creature loses all abilities, it won't stop being prepared, and nothing will happen to its alternative characteristics or to the copy of its prepare spell in exile.