What can I do if my friend passed out after seemingly snorting cocaine. What do I do in this case?

Express how you felt. I would express your feelings about what happened and especially if you had lost your friend. I would ask why they needed to use Cocaine in the first place. Often it is an expression of escaping life's problems. I would then say their are safer ways to deal with life then drugs. Therapy will help get to the root of the problems and healthy ways of responding instead of escape and denial.