How does the bounty system work?
Is there a way to stop a bounty, for some instance that the owner who badly needs the answer had already found it?
Looks like the answer is no: From the info page on bounties
If you're speaking of your bounty question in SO: Is there a way to restrict the external users to access my server files, the answer is NO everytime.
Once you slice off your rep. score, there's no other way to regenerate it. Exception - You could get some score by your posts. I think you've also read SO's FAQ - bounty section.
If you know the answer to your question, feel free to post it as an answer (if it looks good), get the "self-learner" badge.. But, anyways - you can't get back your bounty.