Should you ever replace brake rotors and not pads?

[phillil60]

I bought a 2012 Audi Q5 and it was clear the rotors were bad. The non-Audit dealer I purchased the car from replaced all 4 warped rotors, but didn't replace the brake pads. They told me I had 4mil on the front and 5mil on the back.
Now I have had many people tell me you never replace rotors and NOT replace the brake pads. Audi is telling me now that the rotors have been damaged by the use of the used brake pads.

Please give me your opinion - should the original dealer have put new brake pads on when they replaced the rotors? Is there ever a time when its ok to just replace the rotors?

Thanks for your time and help!