What is the ruling on not fulfilling a vow to abstain from alcohol after the father's recovery, and what is its expiation?

Drinking alcohol is a grave sin. As for vowing to abandon it, scholars differ on this matter: The majority of them hold that such a vow is not binding, and the one who made it must repent, with no expiation due. Some scholars, however, maintain that both repentance and an expiation for breaking an oath are obligatory, and this is more cautious.