I would think, if I were you, that it was time for a serious discussion with your DS 16 as if he were an adult to educate him about alcoholism and the increased risk for him as the child of an alcoholic. I'd treat him as if he were an adult and had to weigh his own risks and his own future. Because, in the end, he will choose for himself.
And I would apply some pretty severe consequences - take away some real privilege that will hurt for a bit. And make sure he knows that the consequences will be real, swift, and painful if he does this again. Because he is still a child, and he needs real boundaries.
ShootingStar1