I noticed that I never updated this thread with the outcome.

I live in the middle of nowhere so I had to send the bag in for service. I believe I sent it to somewhere in the SF Bay Area. The condition of the bag was as described in the first post in this thread.

About three weeks later the back was back. It looks like they somehow reinforced/glued the bottom corners of the bag. The job is airtight, but doesn't look all that great. That said, the bag looks like it's traveled six or seven hundred thousand miles, as it has, so in context the repair is fine.