Smart looking lude.
Provided it's all as per the oem installation, the number plate holder comes off without leaving any holes on the bumper.
Look up underneath the back of the plastic number plate holder (if that makes sense?) and you'll see the heads of 2 bolts looking down at you. Undo them (be careful, possibly seized and the clips will therefore possibly tear out of the number plate holder) and the number plate holder comes off the bumper, complete with the number plate. Provided no-one's bodged anything, that is it and there will be no holes showing on the bumper. Likely to be scratches in the paint though, where the holder has been rubbing against the bumper.
If someone's used normal screws to fix the plate to the number plate holder, it's possible they'll have screwed right through into the bumper and that will leave you with a couple of holes to repair.
EDIT: Arrrggghhh

that damage to the rear quarter is an arse! Have you got the culprit's details to make them pay?