Determine residual value without selling the vehicle?

As I explained in my other post today, I'm waiting for the residual value of my 2005 Audi A3 8P to be determined. Now I'm wondering how this is determined, since I don't plan on selling the car. If I were to sell, the car would be listed on the residual value exchange, and the insurance company would pay the difference. However, since I'm keeping the car, it won't be listed on the exchange. So who determines the residual value? I'm almost afraid that it won't necessarily be in my favor when the insurance company determines it. Someone might drive into my car at full speed, and I'll be left with nothing. I won't be able to get the same car again for 2,500 residual value.