My Uncle decided to drink himself to death. Warned, hospitals, doctors - it made no difference. He was a quiet drunk that kept to himself, and didn't cause my aunt any problems besides having to watch it.
It was an unpleasant and horrible death. His last words when she found him unable to move on the basement floor were "its too late". It makes me wonder how many days he said "tomorrow I'll stop", or if he was just letting her know he knew it was over.
I think there is regret. Its ok until its not, and yes I think they get very frightened when their body starts going haywire. I think perhaps at that time they wish they had quit, but feel the damage has been done - just another reason to keep on.. These late stage alcoholics spend their lives numbing themselves, but they can't numb the death. Its painful, horrible and scary.
I think you are handling it perfectly.