I have a question with a bounty that will expire in a few days. It looks like nobody will get the bounty; only one answer was posted during the bounty period, and it has no upvotes. In cases like this, the bounty is thrown away. Why isn't it refunded instead, if no answerer has earned it?
A bounty is not a guarantee. It's less risky in the new system, but it never has, nor ever will be, a guarantee for the answers you need. It's payment for a bid for an answer, not payment for actual answers themselves.
Remember that although you didn't get an actual answer, you did get 7 days on the Featured tab. If you got refunded, then you could keep your question on the Featured tab forever, which really reduces the benefit that placing a bounty has in the first place.
Basically, consider this like a parking meter - the reputation you spent is good enough for only 7 days. If you need more time, you need to spend more reputation. Of course, it's a parking meter where you can pay however much you want and get the same amount of time, but the extra payment is for the possibility of better quality attention during that same period.
An excerpt from my answer:
Bounties are meant to generate interest and answers. If there are still no answers after offering the bounty, it might be time to consider whether or not the question is too obscure to be answered.
Consider bounties to be paying for advertising. Once you've purchased an ad spot, you can't get your money back just because no one bought your product.
If an answer gets more than two votes and is 'wrong' then you could worry about giving the bounty to the wrong person.
In that case, the best option is to engage the person who answered the question, if their answer isn't helpful to you, then add a comment to it explaining why. Also, if it becomes obvious that your question is unclear then you should edit it for clarity. This has the added bonus of popping you to the top of the active list as well, which would generate extra interest.
Bottom Line: The bounty is to generate interest and answers for your question, it does not necessarily guarantee that one of those will be the right answer.