Bill W. was certainly gravely ill in the last 4 weeks of his life, during which he requested/demanded whiskey on 4 occasions. But it is unlikely he had lost all of his cognitive ability, based on Susan Cheever's account of the period.
It's kind of unsettling to know that the cofounder of AA badly wanted to drink after 36 years of sobriety. But that truth simply confirms the pernicious nature of alcoholism that Bill W. so valiantly fought during his lifetime. The truth does not diminish the validity of AA in any way.
Nor would there have been any diminishment if they had given Bill his drinks. Why they did not do so strikes me as a major ethical, if not moral, lapse. Generally speaking our society looks favorably on fulfilling a person's dying wishes which can reasonably be complied with.