As a multi-decade veteran in the collision repair industry, I agree with the decision of the dealership and the insurance company. This does not come down to parts availability or repairability. It comes down to liability. The part is likely not available because it is part of a larger component called a "space frame". To insure liability protection, GM likely will only service the damaged component as a complete space frame, no repair procedures or parts available. To replace a space frame is in line with constructing an entire new vehicle. To protect from liability issues, the insurance company must adhere to the vehicle manufacturers recommended repair procedures. If none exist, insurance must scrap the vehicle to avoid any further liability issues in the future. In the end, thank lawyers for this issue. They seem to mess up everything for the average Joe.