The sidewall is a sandwich of gel coat, fiberglass mat on luan plywood, foam insulation, then the interior wall. There's very little air trapped in the wall. Delamination happens when moisture gets into the layers and causes swelling or separation of the fiberglass/gel coat/plywood sandwich. It doesn't immediately rot the plywood if caught and repaired. If the plywood is left wet, it will weaken and rot since it's not exterior plywood.
Since you say the accident wasn't your fault, the damage was done to the sidewall by the other driver, not you. If the insurance company want to argue that MORE of the sidewall needs to be replaced than the damage caused by the collision, I think you need to carefully assess how much more than the original collision damage needs repair and pay for that while the other driver's insurance picks up the damage caused by them.
I don't think you will win the argument that the collision caused pressure to burst the wall. Most collision damage I've seen to RV wall constructed like yours cracks or tears open the wall, not popping the skin loose in areas beyond the contact unless left un-repaired and exposed to weathering.