Will I get my promo codes back if I cancel a booking made with the codes?

This would depend on the type of refund being applied.

Full refund

1. Any non-expired promo codes will be returned to your account as long as the refund amount is equal to or less than the cancellation fee.
2. Any expired promo codes won't be returned to your account

Partial/special refund

1. The promo code won't be returned to your account.