This all depends on how the rest of the amp is designed. If the output stage is full of Bipolar transistors then your repair bill could be rather large. Bipolars fail shorted and can cause cascade failures throughout the amp. Unless you see smoked or burnt components it is impossible to tell visually if the BJT is ok or not. Often it is best just to scrap every BJT in the circuit and start over. As far as sound quality goes I have to agree that protection circuits will have no effect. Properly designed ones are not in the circuit path of the sound info until a short occurs. Just having Thermal protection is not the best way to protect your equipment. In the Levinson case Phil's speaker would have been ruined because of the high current value going through the speaker. All amps should be designed with current limiting circuitry for the best possible protection.