We really do not know. That said, with proper care, there is no reason that a bentwood ring will not last for decades. The polymer finish used creates a waterproof barrier to minimize failure in the material. The polymer gives the ring strength. Occasional re-buffing may be required if the ring is subjected to heavy wear or abrasives.
The common short answer to this question is that it depends largely on how they are treated. Due to the specialized hands-on bending technique that capitalizes on the strength of the wood, the rings themselves are incredibly durable. However, any wood finish – particularly on a wooden object that will see constant contact/rubbing/friction with skin – can eventually wear away.