My deepest condolences for your loss,
My 'first' alcoholic was my older brother, an alcoholic for over 30 years. I enabled and enabled and tried to 'fix him' for years. It did no good and impacted my relationships with others I loved and affected my own peace of mind. Eventually I learned and accepted that the best thing I could do for him was to 'step away'. So I did. I stopped 'interfering' in his drinking, stopped lecturing, stopped dropping and picking him up from rehabs. I simply said "I want nothing to do with you when you are drinking". And I stuck to that resolve. 11 years ago he found sobriety, so my brother's story has a happier ending than yours, but even if he had died due to his drinking I would have still believed I did the right thing.
Please, please don't feel guilty. There was nothing you could have done or said that would have changed this outcome. The decision to drink is 100% 'our' alcoholic's, and so is the responsibility for the outcome of that decision. We are nothing by bystanders on their roads to disaster. We'd have better luck trying to stand on the tracks and try to stop a runaway train from derailing. The end result of that would be our own destruction as well as the train's.
My 'current' alcoholic is my esDH (estranged DH). I am taking the same stance. His decisions are up to him, I won't stand in his way. I've accepted that if/when he dies as a result of those decisions, it will in no way be my fault.
I wish you peace. And we'll always be here if you need us, even though he's gone now. The 'traces' of pain they leave behind don't leave us. We just learn to live with them.