Turbo Waste-Gate

I got my '99 Passat chip diagnostics done 3 weeks ago, I had to have the waste-gate re-soldered down and two vacuum lines replaced in the turbo. Just last week someone rear ended my car, after which the engine started making a strange noise on deceleration. I put the car back in for servicing with the dealership to find the problem. The dealership said the waste-gate and/or my oil pump to the turbo was broken causing my turbo to break.

If the waste-gate is broken on a turbo does it make a strange noise on deceleration and would it cause the turbo not to work?, and if the oil pump is broken causing my turbo to seize wouldn't I smell it burning and the chip register it on my dash as a problem? (which neither has happened). Is this a mechanical fault of the dealership or caused by the accident, neither myself nor the insurance company are sure.