First, my condolences on your loss. I lost my dad this last March to lung cancer. He started smoking in the Navy in the 50's and even though he managed to quit about ten years ago the damage was done. I think we got five more years with him because he quit which turned out to be the best five years because we did a lot of hunting and fishing together so I really got to know him. We were not that close most of my life.
All that aside, addiction is a usually a physical manifestation of mental issue; low self esteem, depression, stress, inability to cope, etc. People find it easier to self medicate than to get the real help they need. It is our job as friends and family to do what we can to give the love and support. You can't save them all. Some people are just hell bent on that path of destruction no matter what you do.
My Bro-in-law in on that path and it is killing my wife because she is his big sis and there is nothing she can do. Forgive the rambling but this is one of those things in life where there is never an easy answer. My thoughts and prayers are with you Poobah in this difficult time.