What causes a complete electrical shutdown, system widow, during a time when oil pressure was very low, or zero?

I've just experienced a complete electrical shutdown after driving my 1997 Nissan Quest van with little to no oil pressure. My son had the van out the previous evening and had ran it all night to stay warm while working as a security guard. this morning, I was in route to a grade school when I noticed the oil light was staying on constantly. I then noticed that the engine would make funny noises (such as a light knocking) the more throttle I gave it, the noise increased. I babied it to the school and when I turn to go up an incline at the school, the motor just switched off. Approximately 30 minutes later I came back to the van after adding 3 quarts of oil (i needs 2 more) and tried to start it. I heard one click then the entire electrical system was dead... no power to anything when the key is in the on position. It's just as if there is no battery. I checked and there is a good charge on the battery, terminals are also tight.

I've heard these vehicles are designed to shut themselves off in the event of very low oil pressure. How do i restore the electrical system?

Thank you.