Hi all! Sorry for the late post.
We got an invoice from the cleaners for the extra charge, referenced the lost key charge in the house rules and are working on getting a quote from our handyman. New guests checked in hours after these last guest left, so haven't had a chance to get the handyman in without disrupting our current guests. We submitted the lost key and the cleaner's' invoice to Airbnb and are waiting to submit the broken wall invoice. Airbnb support was essentially non-existent. Way too much time spent on chat and on the phone with really no help so next time, won't bother.
We left a bad review for the guest and texted the guest to ask them if they know where the lost key is and let them know that the house rules were not followed. Never heard back.
We do have all electronic locks except for our patio door, which is the most convenient way in/out of the main house. Unfortunately, we spoke to a locksmith back when we started, and electronic locks will not work on this patio door.
I'm going to add a refundable security deposit for all rentals as well and possibly charge $50 non-refundable fee to cover any small items that happen like this in the future.
Thank you to everybody who responded.