We have a Gates CDX on our tandem. Never had a problem with it in many thousands of miles. The rings will get worn before the belt. I expect at least 20,000 miles out of the setup, judging by ring wear so far. Of course in our case a bike shop could fix us up with regular rings and chain if it came to that.
Of course there's always the chance of an accident or picking up debris in the drivetrain. However that's never happened to me in decades of riding with chains and a belt. In any case, no show-stopper. Overnight shipping is pretty quick. Don't worry about it, don't bring a spare belt.
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