I'll bet the real answer is "nobody knows". As an early adopter, you are the testers. Is this belt your timing belt (or the drive belt)? If it is the drive belt, the most likely early failure symptom would be for the belt to begin to slip on the smaller sprocket. If it is the timing belt, there are so many teeth in mesh (180 degree wrap) that it is very unlikely to slip. Timing belts in car engines will eventually break but give essentially no symptoms until that point. However, that is a rubber belt on aluminum pulleys. Are these pulleys aluminum or plastic? If aluminum, I think it would take a very long time to see any failure symptoms. If they are plastic, I would guess that the pulleys would wear out before the belt. Each pulley tooth meshes with way more belt teeth than any one belt tooth meshes with pulley teeth.