2000 Other Mercedes Benz Models motor damage from no oil

I recently had my motor oil changed at a oil changing service center. Unfortuately, they forgot to replace the motor oil and I drove home approximately 6 miles with no motor oil! The motor was making loud noises and I had it towed to the mercedes dealer the next day. The mechanic had replaced the oil and reported that the car was running o.k. They didn't run any diagnostics on the motor and said thers was no guarantee that the car wouldnot have any problems later. I don't want to accept the car knowing that certain internal damage has already occured. What kind of damages should they be able to find if they were to fully inspect the motor? What are my options as I am uncertain about being burdened with an enormus expense.