How do you deal with the death of a father when you had a terrible relationship with him?
I want to address two traps:
Becoming free does not require the other person's cooperation.
Becoming free does not have to be done before the other person dies.
Forgiving the unrepentant. You have already paid by being your father's child. You paid with suffering, confusion, humiliation. Perhaps, as I did, you paid with bruises and blood.
Healing is how you collect what you paid for. Insight, compassion, release, a wicked sense of humor, abiding peace, the determination not to repeat his mistakes - these are the jewels embedded in the walls of the cave you born into. Be sure to gather them as you walk back out.
It's compassionate to want your father to leave the cave as well. It's certain that the little boy he once was found himself suffering in ways that mirror the things he did to you. But if he is not willing or courageous enough walk out with you, it does neither of you a service to stay in darkness with him.
In fact, as you walk toward the light, generations of family pain trail you into freedom. Your father, so accustomed to your proximity as a release for his pain, may follow you a little way up - as my mother did - or he may stay bitter and hard. As you near the surface you will still hope for his apology, not because you need it - but because you see how withholding it blocks his release.
Dying without resolution When I was young I thought a sense of urgency was important to get healing work done. I was fond of telling myself and others to seize the current opportunity. I said things like "if you don't learn this now, it will come back harder." Now I say, "if you don't get this now, it will come back - sometimes harder, sometimes easier - it will come back." Today I see this opportunity to take another swing at these most important lessons as grace.
Once you set out on the path of healing, everything that happens supports you on that path. The act of writing this questions, the act of thinking about writing this question, this is not you "preparing" to deal with your father, this is the actual work. If you heal your relationship with your father while he is alive, that will be one path. If he dies and you two are not ok, whatever you experience as a result of that will be folded in, part and parcel of the healing you continue to do.
This work is hard enough without the illusion of too-late and the exhausting taint of despair. The doors to healing open inward. Relax, step back, don't push. There will be time. But the doors don't open on their own. I encourage you to summon up your best self, to be self-gentle, to be self-compassionate, but also to be fearless and when you have the energy to proceed to see what you can learn from the being of your father's child.