Since my dad's passing three weeks ago, I have been through different types of days. Some where I feel OK, like at 93 he had a good run, to days where I see his empty chair at my parents house and lose it. Or today, where the issue du jour seems to go back to the evening he passed. The nurse called at 10:30, saying he began going downhill at 7:30, and thinking, her next sentence will be, you should probably come down. I was already standing up to grab my jacket. Instead, she said, he passed at 10:22. I didn't think about it much at the time, but when I was at the NH I asked her why if he was going downhill at 7:30, didn't she call me. She said she didn't think it was that bad, so it was her fault. Not a real explanation in my mind, just a mea culpa. I said its not her fault, but as I was thinking about it today, I got very angry. Did she really not think it was that bad, or just not take the time to call me earlier? Had I known, I would have gone there and called my mom and brother too. Then I begin to think it was my fault. Before I left that day around six, I should have told the nurse emphatically, if there is any change at all to my dad's condition, not matter how minor, call me right away. So I go from feeling guilty to not doing that, to the other extreme, thinking I would have just assumed they would have called me so I didn't tell them that, then they dropped the ball and didn't call me.
I guess I do have some anger about that. On the other hand, this could just be how my grief is disguising itself today. But if she knew my dad was going downill at 7:30, she should have called me.
I had so many questions and was driving myself crazy with the 'what ifs' after my grandpa died. I agree with GardenArtist that therapy will help you to heal and be able to make peace with your father's death.
There are also grief support groups in most major metro areas. I would reach out to them as well. You need as much support and counseling as possible right now.
It sounds like you and your dad were very close, and I'm sure he would not want you to beat yourself up over the 'what ifs'. He would likely want you to take care of yourself and know that he is at peace now.
Sure, grief can manifest itself in different ways. It's a challenge for anyone for work through post-death grief, but dwelling on a particular issue, one over which you had no control, really doesn't help you get past the loss of your father.
In the long run, how would an alternate notification have helped you? As some of us mentioned, sometimes people who are dying don't want their family to be around; they want to spare family members from the grief of seeing a loved one pass. And who knows what else they may feel? We'll really never know.