Ihcho,
Have the transistors been destroyed? It’s really grainy from the photos;
Since many of them are connected in parallel they all experienced significant current ( if actually shorted at output), but due to device tolerances, in the event of a short, the devices and emitter resistor combinations with lowest resistance will go poof the fastest; the emitter resistors on all output transistors of the compromised channel should be checked as well because even small changes there can really affect the distortion profile of the output stage.
If this were my amp and such a thing happened I would probably end up rebuilding the output board; Pain in the ass yes, but then you have a factory speced unit once again.
Did you examine the speaker connectors for evidence of arcing ? Black carbon, deformed metal etc...