While my dads old M3 was at a garage someone dinged the rear bumper, as a matter of corse my dad was notified, they said they would replace the rear bumper and have it back to him asap. It is a matter of pride, service and reputation. The dealer did a great job and was back to my dad within a week. Although he wasn't happy they did everything they possibly could. Which in my opinion is what they should do.
I doubt any insurance will get involved and they will repair the damage in the same manner, otherwise get in touch with trade standards or give BMW head office a call. They will want to get this swept under the rug ASAP as it is a complete embarrassment to the dealership and the reputation of BMW.