Dad is gone

My dad died ten days ago of pancreatic cancer. He was diagnosed with stage 4 cancer only less than 4 weeks earlier. He went from living a happy life as a retired man to knocking at the hell's door. He stopped eating as soon as he started to have symptoms. He did want to do chemo but felt too weak. Doctors said he was not a candidate considering his status. I saw him declining day by day, I saw his pain growing and changing with time. I saw suffering no creature should experience or see experiencing. He spent the last 4 days at home. We told him he was going to come back home to recover a bit before starting chemo. It was a lie and he knew it but pretended it wasn't. He did not have the time to cope with his condition and process it. I spent those last days with him in bed listening to his loved music. I could see him following the rhythm with his fingers or commenting on a song when pain and morphine allowed him to be present. I was the one next to him when he took his last breath and I went to tell my mum and sister he stopped suffering. As much as I and all the family were relieved to see such suffering ending, I am now devastated and heartbroken beyond any help. I am struggling to cope with my daily life.
Could I have done more? Was the prescribed medication we gave him correct? Could have been another way to get him to his ending a day later? Will I ever get over the fact of having helped him to die when the only thing he wanted was to live?
I do not have the answers to this. I just feel sad and broken. I live abroad and I miss my family now. Life goes on but I miss a piece.