Natural Justice would be him being challenged to a duel by her brother or shot by her father. Patriarchs are the Justice of the Peace, if there are no official paths to enforce her contract.

The idea that a man can just leave her high and dry and walk away is based upon the error that other men have an interest in allowing him to leave, unscathed, leaving them to provide for an abandoned woman and not even giving them the satisfaction of exacting retribution.

Contracts with women are always de facto contracts with other men. Courts are a gentlemens' agreement, so eliminating courts just means men have to get the swords and pistols out, again.