Hi! Welcome to adult children. I am so sorry to read of your dad's troubles. I can understand how he feels. I was once depressed and trying to drink myself to death as well. I hit my bottom and surrendered. I got better, but the depression is something I will always have to take care of. For me it means lifelong medication.
Since you have already spoken about it to him before y poo u know it does nothing. It won't. If merely imploring to our alcoholics worked there would be no alcoholics. Everyone who has ever loved one has been there, done that.
You can tell him you love him and worry about his health but that's all you can do.
Getting yourself into Al-Anon can be a great support for you