Don't feel guilty about anything. Just don't. I know it's painful but If an alcoholic get's him or herself killed because of their addiction, it is no one's fault but their own. More than anything, they had it coming. It may be a harsh way of looking at it but it is the only way that I personally can deal with the pain, hence why I recommend it.
I read a story once where a son had to walk his drunken mother home every night from a bar, all the while being verbally abused by her. One icy cold night, on the way home with his mother, she fell and couldn't stand back up. Frustrated at the fact that her son let her fall, she berated him and told him to get lost. Her son, fed up with her mistreatment of him, decided to do just that and so he left her. The next day, the son woke up and found that his mother hadn't returned home the night before. He finds out that she died in the cold. The son feels crushing guilt over what he had allowed to happen.
When I read that part I thought to myself, "He shouldn't feel guilty for what she brought on herself. She's not dead because he left her, she's dead because she had gotten drunk and repeatedly mistreated her son. This is her just deserts." Again, I realize that this is a bitter, resentful way of looking at it but it is either that or feel depressed over it and I'd take anger over sadness any day. At least anger can be turned into strength.