I don't understand what the "How is a bounty awarded" section doesn't answer this entirely:
After the bounty ends, there is a grace period of 24 hours to manually award the bounty. [...]
If you do not award your bounty within 7 days (plus the grace period), the highest voted answer created after the bounty started with a minimum score of 2 will be awarded half the bounty amount (or the full amount, if the answer is also accepted). If two or more eligible answers have the same score (their scores are tied), the oldest answer is chosen. If there's no answer meeting those criteria, no bounty is awarded to anyone.
It's not uncomplicated but in the simplest terms it goes in the order:
- Whomever the bounty-setter picks, if they do it within a time limit.
- The highest voted new (after the bounty was created) answer is automatically picked, if there is a +2 scored new answer.
- Nobody. The spent reputation fades into the ether.