I think the bounty/reputation should be preserved for the answers even after the question is deleted.
There are specific conditions in which rep on deleted posts are preserved:
First, if you’ve contributed something worthwhile to the site, you should keep the reputation for that even if it eventually gets deleted. “Worthwhile” here is defined as,
- A score of 3 or greater
- Visible on the site for at least 60 days
It is kind of not fair sometimes.
Well, nothing's fair in this world.