Is it permissible to lie to cover for a father who drinks alcohol, by saying "he has quit drinking" or "he has repented" when people ask about him?

Lying is forbidden except in specific situations, including reconciliation between people, during war, and in spousal communication. Analogously, this includes lying to conceal someone else's property from an oppressor, or denying a sin to cover oneself or others, as long as the person is not openly defiant. Therefore, you should advise your father gently and kindly, and explain to him the prohibition of alcohol.