good answers.
That's what I ended up doing. Before they left, one of them started a fire which will burn most, if not all, the wooden structures and blacken the rock. So I decided that IF they make it to the end of book one and notify the swordlords about the bandits being taken out, they can build (rebuild) the keep with a few BP leftover, instead of the full award.
They should make it through easily, as they started the campaign with 4th-5th level PC's. I've toughened the encounter to give them a challenge and not awarding them XP for exploring. I couldn't toughen up the Mites and Kobolds though.
So a follow up question on BP's, when book 2 begins.
Should the DM notify them of the BP credits at each area they have explored. i.e.
1. Nettle's bridge
2. Fort
3. Temple
ect......