The only rule is that the in-laws must return the bride-price. In chapter 10, the egwugwu are introduced. They sit as judges for all matters of the Ibo court. They hear a case in which a woman has escaped her husband, and he demands the bride-price returned. However, he treated her so poorly during their marriage, even beating her while she was pregnant & when she was ill, that his in-laws see no reason to return her or the bride-price.
The interesting thing about this case is that the egwugwu rule in favor of the wife and her family, and against the husband. But, we know that one of the judges is Okonkwo himself, who regularly beats his wives. It is clear that spousal abuse is a crime in the Ibo community, & Okonkwo fiercely believes in the laws of the village, even so far as to rule against a man who has broken one. Yet Okonkwo himself breaks this law as well. This reveals the paradox in his character.