I just heard a piece about this on NPR last week. If
he breaks it off, which seems to be the case here, she gets to keep it. If
she breaks it off, it goes back to him. It's a
conditional gift, based on a promise. Whichever side breaks the promise is the one to lose the ownership of the gift.
Still, rules may vary from state to state, so
Socal's advice still stands.