Pretty much a moot point, as neither of them were very bright to begin with, and obviously cannot spare any of the brain cells they lose. Also, the real damage may not manifest in ten years, rather it will appear when natural degeneration is more pronounced.
I have to weigh in on this, seeing as my name refers to my feelings on drinking…
I honestly think that, as it was said before, if you’ve been smoking up or drinking consistently for 10 years, then neither person is very bright and both will be relatively less intelligent. That said, I think the drunk will be worse off.
I say this because alcohol is very addictive. My father is a career alcoholic and has no intention of quitting. Sure he joined the AA bandwagon for a few years, but it didn’t stick. During those years he was promoted and actually became a manager at the office he worked at. He was very productive. His social life improved and he became a marginally better father (he was still an asshole.) Then he fell off the wagon (about 5 years later) and lost his job, lost his friends, and lost his sense of humor. He became increasingly abusive (verbally and mentally.) He was less interested in literature and the arts (whereas when he was on the wagon he had expanded his pallet so to speak.) There was a marked decline in his mental abilities.
Now his brother, on the other hand, was a life long pot smoker (he did dabble in other drugs though) and he was never very intelligent. I have a million and one stories about this dumbass, but the point is he was born stupid, grew up stupid, and has remained stupid throughout his pot smoking adulthood. He was never very smart, but his intelligence has not markedly decreased since he started smoking up.
Sorry for the diatribe, I just wanted to point out two case studies in my life that demonstrate the destructive power of alcohol.