If my XH had a big purple neon sign above his head flashing "DANGER AHEAD, ALCOHOLISM IN PROGRESS", I still would have married him. I married him despite *all* my friends misgivings, and I married him in secret so that my family could not protest. It took A LOT for me to realize that I was married to an abusive alcoholic who was slowly chipping away at my sense of self, but when I did, I did it on my own.
As much as your friend plainly has no control whatsoever over her boyfriend, you also do not have any control over her. You asked if you "can" threaten her....to answer you, yes, you "could", but it would get you nowhere, except perhaps alienated from your friend.
You cannot MAKE her come to any realization, just as she cannot MAKE her boyfriend stop binge drinking. If you have serious opposition to her boyfriend, then state your boundary ("i.e. I refuse to be in his presence if he is drinking"), and then let it go. When and if your friend is ready to make a change in her life, she will. Until then, it's her business.