I have several questions. Would xtreme cold (-10) contribute to a turbo failure? How hard is it to replace turbos on a 2000 A6? Is engine removal required to complete this procedure?
Turbo replacement on 2000 Audi A6 Quattro
As an aside the turbochargers can only be replaced in pairs since they are computer matched. In addition there are several critical components such as oil lines that must be replaced concurrently.
Changing the turbo chargers on this engine requires taking out the engine about $3000 total retail cost for the turbo chargers, about 3 hours to swap out the turbos once the engine is out and probably 20 hours to pull out the engine and reinstall. Extreme cold would not "cause" the turbo chargers to fail, infrequent oil changes, or use of poor quality oil would cause premature failure. Use of Synthetic oil in these engines is important. Before assuming the worst see if there is an Audi specialist or dealer in your area to get an expert opinion.