If you do decide to try an intervention, you have to know that the only chance it has of being effective (and personally, I think this is a very slim chance at best, but just MHO) is if all parties involved in the intervention are willing to define specific boundaries and stick by them (i.e., 'I will no longer make excuses for your behavior when you are drunk,' or 'I will no longer allow my children to be around you when you are drunk,' etc.). Interventions are more about the people around the A than the A. They need to be as ready to make big changes as they are asking the A to be.
Empty threats will likely just make the situation worse. An intervention will fail - either in the short- or long-term - if it's used as a tactic to try to scare someone sober. And a bad/not-very-well-thought-out intervention (like the one my mom's sisters tried on her) will just cause major resentments from everyone.
A true intervention consists of the important people in the A's life coming together to tell the A that they are not gong to support their lifestyle anymore. That they have had enough and are taking control of their own lives now.
If even one person in the bunch reneges or falters, the only result is that the A learns he or she does not have to change, that they will always have someone to support and/or enable them.
If you decide to go forward, please consider consulting a professional to walk everyone involved through the process. Good luck to you.