Sorry. Got interrupted.
Hi.
If your dad was drinking as much as you stated in your original post, then it is likely that, having picked up again, he will go down that road again.
There really isn't anything you can do, as this is your father's choice.
I know you are worried. May I suggest Al-Anon meetings?
It's a fellowship for people who are troubled by a loved one's drinking. There are meetings everywhere, and online support as well.
Peace.