Chris,
I am so very, very sorry. The outpouring of emotions will come... I think our brains and our bodies and our emotions just take time to catch up with reality.
The degree is so different and I know this... but my Grandmother died a few months before my Mom did... I had promised her we would go see her as we had moved closer to her (only 10 hours instead of 20), but since I was pregnant and had been travelling so much already we put it off... then she had a stroke, and a bleed, and we lost her... And I only had those moments with her in the casket as well. It hurts so very, much. And it's a terrible feeling of pain.
Your dad knew. He knew how much you loved him. He knew you would have been there if you could, and I suspect he even knew you were there with him when you were.
Most of all, I'm just so sorry.