The following question for example: Coupon calculates but doesn't sent correct amount to payment gateway (Cybersource) doesn't look like its going to be answered CORRECTLY. Now obviously a "correct" answered is determined by the person who asked the question. But in general, Does the bounty return to the issuer of an unanswered question or does it stick to the question eternally?
If you don't accept any answer, or assign the bounty to any answer, and there aren't answers with a score of at least 2, the bounty is not awarded. As the FAQ says, in such case the bounty is not returned to who offered the bounty.
In any case, you will always give up the amount of reputation specified in the bounty, so if you start a bounty, be sure to follow up and award your bounty to the best answer!