Sweet girl, You have done such a good job of helping your dad - devoted and loving. Having been there with my husband, we all think we could have done better. Yet we just are not perfect caregivers - and we do not have the power to hold back death for anyone. We only have the power to love them through it. And then love them some more.
Remember that your voice of reassurance that Jesus is beside him and will help him through this time, and the touch of love through your hands are exactly what he needs now. He also needs to hear that you will be okay.
A verse that ministered to me when my husband died was this one: Ps. 116:15 "Precious in the sight of the Lord is the death of His faithful ones."
Now, place your right hand on your left shoulder, and your left hand on your right shoulder and squeeze. A hug! Know it is from all of us here.