To answer your question...
1. They do not. There is a return policy (30 days for refund, 90 days for store credit I believe.)
2. If you are out of return, you can trade the ring in on something that is at least double the sale price of the ring (i.e. if you paid $5K for the ring, you can trade it in on a piece that is $10K or more.)
3. If you are in CS, let me know... I know a wonderful young lady that works at the Zales in Post Oak that will help you if she can.