Help! How long can you ran a Chevrolet opera without oil?

I have a huge problem, my brother was driving his car (opera chevrolet) to my house when he couldn't avoid a big rock that was on the road and made a huge hole in the oil pump, because there was no place to stop in the road to check the car, he ran the car for 5 minutes approximately until he found a gas station where to stop. When he noticed what have happened to the oil pump he called the tow truck to pick him up.
The chevrolet Agency had the car for 1 month repairing the damage. Finally, when they told my brother he could picked the car, they made a final test and they found out that the engine had a problem. Now they don't want to repair the engine because they said my brother ran the car with no oil.
So, my question is, How long can a chevrolet optra run without oil? How much time can you run a chevrolet optra without oil before making any serious damage to the engine. If I can prove that the time (5 min) my brother ran the car to the gas station does not represent an important factor in the damage caused in the engine, the chevrolet Agency will pay for everything and my brother will be excused. Thank you very much for your help. Waiting to hear from you.