I recently placed a 50-rep bounty on a question, which received no additional input.
Is there anyway to reapply the bounty or do the rep points evaporate?
From the FAQ on bounties:
If you do not award the bounty within 24 hours of the bounty period ending, half the bounty value will be automatically be awarded to the top voted answer posted after the bounty start, provided it has a score of at least 2. If no new answer matches this requirement, no reputation will be awarded at all, and the reputation used on the bounty will be lost forever.