I haven't gone on my trip yet. I decided that I was worrying unnecessarily, and I would take the belt-drive bike and leave the spare at home. It's not the bike I usually ride, so I wanted to intentionally get out on it a few times before the trip and make sure everything was in good shape. To that end, I commuted on it yesterday. Or tried to. At one point I gave a good push on the pedals and found them spinning without moving the bike forward. I thought my Nexus 8 had given up, and I'd finally get my wish to replace it with an Alfine, but when I got home, I found the rear Gates track cog was quite destroyed at the point where it interfaces with the hub.
A replacement is around 80USD, which would be fine if it was a dependable part. I just replaced a chain cog on my main bike that has worn out after 4 years of heavy riding, whereas this bike has had 3 years of light riding. The cog I replaced didn't fail. It just started skipping. I was still able to finish the last 100 miles or so of my tour before replacing it. Whereas the Gates cog showed no signs up trouble until suddenly the bike was unrideable. I just went ahead and ordered the parts I need to convert the bike to a chain. New chainring, new cog, two new chains came in under the cost of one, new Gates cog, and I expect the set-up to last longer. Maybe this break is just a fluke, but it came right as I was planning a trip, and I don't want to deal with "maybe it will be okay" when heading out for a week of riding.