Question: At the end of the movie when Joe goes to live with Santa and the elves at the North Pole, what would happen to Cornelia (the girl Joe and Santa befriend) after she stayed there until the next Christmas? She would have no one to look after her when she is taken back to New York, since her only relative, her step uncle floated away after eating Patch's candy canes to evade arrest.
Answer: She did have her nanny. She may have been strict, but was still fair, especially after eating Patch's lollipop, feeling like Mary Poppins, much to both their amusement.
Answer: She most likely would have stayed with her aunt. It was said by her nanny that B.Z. was her step-uncle so she definitely would have family to go back to.
Question: How did Santa, Anya, Donner and Blitzen get to the North Pole if they passed out?
Answer: They were magically transported there.
Chosen answer: We don't know for sure that the uncle is her only relative, he is the only one we see in the film. She may have other family in or around the city that she may live with after her return.