there is a scenario in which the engine problem can be solved with a power reduction...thus reducing the bleed air leak to levels below the fire warning requirements.
I've flown P&W on both the dc9 and the 737 and both had similiar concepts...if the warning stops with power idled, you may leave the engine running.
however, this one seems to be a fire as the bottles were shot and the fire department foamed to stop the remaining sparks.
I also think I wouldn't have evacuated via slides for the situation as we presently see it...more danger of pax injuries
I doubt anyone will read or respond to this post as I seem to be censured.