I knew it is really painful on everything your dad did in his own family. But he is still your dad. Maybe he wants to be alcoholic throughout his life because he is condemning himself and wants to "forget".

Go and see him. If you already forgave him on the abuse he did to you, then tell him. I hope that would gain a relief to him. Just show kindness before it'll be too late. You have my support and I supposed all the people here in PC. Give us an update when you get to see him.