Hi - and my condolences about the prang. Even with Parktronic it's easy to misjudge reversing as I know to my cost when I recently hit a rail that was higher than the sensors.
Your rear bumper is all one piece of plastic. If the surface is punctured, I don't think that it is repairable - apart from minor paint scuffing which could be resprayed. You can often see them for sale s/hand on eBay. However that would likely still entail re-painting.
The bumper removal job looks a reasonable DIY (with a helper) but you will note that the inner fenders have to be loosened to get access to bolt 2.
I have included WIS diagrams for both rear bumper & rear inner fender removal. I'm not sure about the rear SAM unit and why it has to be touched.
(continued below for rear inner fender removal)