I pity the FOO!
WilliamJ, I get what you mean about the higher power thing. I never went to al-anon meetings, for that and other reasons, but I have done a bit of reading and the stuff about "detachment" has really helped me. (My husband is alcoholic.)
So maybe some therapy/reading for your wife along those lines? The hardest thing is that alcoholism perverts the natural urge to help loved ones. There's the question of will at the heart of alcoholism, so that unless he has the will to stop, all her efforts to help will be futile.
You sound like you've got a good handle on it all--strong boundaries, a good BS detector. For all that you and your wife argue about it, I bet on some level she's grateful to have that sanity-check. Because yeah, your future together is more important than some old nut who's out to kill himself in the most long, drawn-out, obnoxious way possible.
And you're right: if he moves in with you, or if you guys buy property solely in order to live next door to him, then the marriage is over. That's not an ultimatum, that's a fact. She knows this too, even if she's not quite ready to say it.