Don't give up.
When I was in the Critical Care Unit (CCU or ICU) post-op, there was a man in his late 70s or early 80s two beds over who was on a ventilator and was still unconscious from his surgery. I have no idea how many days he was there before me, but for the three days I was there, his wife, son, and daughter would visit several times a day and talk to him. It was heart wrenching to hear them call out "Pa-Pa, Pa-Pa". I couldn't see him but the entire time I was in CCU his family came regularly and passed by my bed. I left CCU wondering why they didn't just let go. After three days I left the CCU and spent about 2-3 days on the regular nursing floor. Due to my own complications I was sent back to the CCU and he was still there and unconscious but now without the vent tube. This time I was across from him and could see his visitors and his family who continued to visit. I thought it seemed dismal since he was still there a few days later when I left CCU the second time.
Now here is the good part. One day while walking around the nursing floor after leaving the CCU I passed a room with him and his family. He had regained consciousness and was moved out of CCU! He was still surrounded by his family and was apparently aware and communicating. I was very touched and being somewhat emotional due to my own situation, I had to go tell him how I had watched his family stay committed to him. His son knew me from the CCU and I asked if I could speak to his father- he agreed but had to translate what I said. All I could think of to say was "You have a good son and daughter and your family loves you very much". I guess I meant it for his family to hear as much as for him to hear. He was still recovering from the vent. tube and couldn't speak very well, but as far as I know he was recovering well when I left.
I hope and pray that your Dad continues to improve. I know his family loves him very much too.
Take care,
John