The short of it: There are no reliable solutions. There are no good answers.
People with depression and substance abuse issues don't think the way non abusers do. They know what they're doing is wrong and that it could lead to death or going further down the spiral, but their ability to rationalize their behavior is all powerful. It has nothing to do with will power or motivation. There's something wired differently in the brain.
Medication, AA, NA, inpatient treatment, religion are all good things to try. Sometimes one of them sticks. I wish you the best of luck. The only advice I can give is this: If something bad happens with your father, it is not your fault. There is nothing you can do to change his behavior. All you can do is be supportive if he recognizes the need to make a change.