Don't beat yourself up, you coudln't have made much difference. Console your siblings especially your brother who is probaly feeling a lot of guilt for your dad's situation.
I didn't get to say goodbye to mom except for frank discussion about her advancing diabetes sitution a week before she passed suddenly.
Dad took it hard and basically packed it in. He told doctors he wanted to die, doctors told us doctor/patient confidentialty ruled, and dad told some good lies and put on big act at hospital. By the time I figured his game plan dad was in hosiptal for 5 days. Dad didn't realize how close to death until we told him he only had about 3 months to live max on day that he died. His cooperation just came a little too late to get him home to die on his own terms.