Crappy,
The problem is that the fans aren't fed from the same power supply as the B+ and to make everything contingent upon the fans starting up would probably mean rewiring the whole amp, which isn't even an option with the pcb. Or if it is an option it's one hell of a coincidence.
What might be more appropriate is to have some sort of thermal fuse on the AC inlet, but I'm not sure they much such a device that would be sensitive enough yet not too sensitive.
Bottom line, if it were my amp I'd take the occasional casual glance inside the chassis to see how the caps were fairing at a minimum.