I am a recovered alcoholic and last summer I met my neighbor who told me she is leaving her husband because he started drinking again after a year of sobriety. He hit bottom fast, and she told me he was spending hundreds a week on alcohol.
My sponsor suggested an intervention, but when I raised the issue at a couple of my AA meetings, the guys told me: if he doesn't want to, there is no point.
I think an intervention does work, but there has to be willingness on the part of the person.