I’ve been out of the service business for 20 years but we used to put a load on batteries with a VAT machine and see if the alternator output picked up to compensate for the load. If the alternator has no output the load on the battery would kill the engine. I may be a dinosaur however.
Agreed. I was taking this "bad diode" too literally.
Certainly, if system voltage sagged enough, even the coils in the RCM will loose enough energy that, even if the injectors, ECM and other stuff managed to keep going, the engine control relay (and others in the car) would release and the car engine would stall.