I would certainly buy liquor for an elderly person who has conscientiously chosen his/her way to go.
One of my friends knows an 80 year old woman, who can no longer drive because of vision and other health problems. She has lots of money, but her children refuse to take her to buy liquor and cigarettes. So she has my friend take her every Wednesday to the liquor store and to buy cigarettes. She buys a carton once a week, so is smoking quite a lot it seems, and she buys a gallon of whiskey or vodka and several bottles of wine the same day, each week. Her children live near to her but my friend has to drive 10 miles each way to do this for her, simply because the woman's children won't do it for her because they don't think it's good for her. Of course the woman is an alcoholic and smokes too much, but she is 80 years old, not a good age to go through withdrawal or try to change habits. I say buy her vices and let her be happy for the short time she has left.