have you inquired about ultrasonic treatment, where ultrasound is used to break the stone in little pieces, and your urinary tract will expel it once you urinate. If the ureter is not completely blocked the risk for kidney damage is small, and you might even expel it naturally.
I think this is a rational concern. Yes, kidney stones can cause damage to the kidneys. Not all the time though. It can cause the kidney to atrophy, thin and not function as well. Or an infection can happen related to the stones. But, when the damage happens, it is usually when the stones are not detectible in terms of symptoms. The person doesn't have pain so they go a very long time with the stone. You had pain and are scheduled for surgery. They wouldn't risk damage for you so must feel it is okay to wait.
My guess is there will be no damage and hopefully you get your surgery soon.