I heard back.
He's been "ill", and didn't get to check his emails. He "didn't want to worry" me any longer.
He sounded very depressed, which was a major reason we fell apart. He talked about depression and suicide all the time, but didn't want to do anything about it, other than to pop an antidepressant that wasn't working and to keep drinking. Suicide is now off topic--despite the fact that I lost two A brothers to it. He can also be very UP at times. Not up to me to diagnose, though.
Previously, this would've been my cue to jump in and try to fix things--offering as much compassion as I could muster and trying to find the words that would be the magic key. One time, I went too far in trying to help, and I had to make an amends. (Keeping my side of the street clean.) This time, I just listened but didn't comment.
He says he'll call later to set up a time to work on the event. I'm not going to attach any expectations to that either way.
If he doesn't show at the event, I'll say nothing unless asked. If I am asked, I'll reply, "He could not attend." If they press further, I'll just change the subject or something similar.
Fortunately, he hasn't shown to events drunk; but I realize there's always a first time. Better to avoid inviting worry and trouble in the future.
Thanks for all the experience, strength, and hope.