4 ideas
The villain Capricorn, his henchman Basta and the fire-juggler Dustfinger stepped out of the book, and Resa disappeared into it. Mo then never read aloud to Meggie again and moved from place to place with her, hiding the gift that had cost him his wife until Capricorn's men tracked them down years later.
In the novel, reading a character out of a book forces an exchange: something or someone from the reader's world is drawn into the book in its place. The reader does not choose what is taken. The gift can therefore never be used cleanly, and each act of creation is also an unpredictable loss borne by someone nearby.
Dustfinger is stranded in a world without magic, desperate to return to his own story, and he will betray anyone who might send him back. He also refuses to hear how his book ends, because he suspects it holds his death. Read through him, homesickness includes wanting a place where your fate is already written and fearing to learn what that fate is.
Capricorn is finally defeated when Fenoglio, the author of Inkheart, writes new words and Meggie reads them aloud. Neither can change the story alone. The novel holds that stories are not fixed, but revising one takes both someone who writes the words and a voice that gives them force.