Detecting a loss in mass air

I have a stock R33 GTR. Like most 20yr old turbo cars have likely experienced, I was driving spiritedly one day when the coupling on the intercooler inlet popped off and all my boosted air was escaping to atmosphere

Imediately the car ran terrible and plumes of black smoke went out the tail pipe as I nursed it home.

I would like to confirm why this happens and also ask if there is a way to keep it from happening (likely with a standalone ECU).

My assumption on why it happens is the air is metered by MAFs right after the the turbos, then escapes. The ECU assumes all that metered air will go into the engine, so it enriches the fuel. But since it doesn’t make it, it ends up extremely rich...

I’m also guessing that with a MAP based system, this wouldn’t happen since mass is calculated based on the pressure in the plenum... of course there would be a major power loss...

Finally, I assume the stock ECU cannot counter the richness using lambda since it’s in open loop?

do I have this right?

If so... does functionality exist on standalone ECUs to detect extreme richness/leanness and protect against over/under fueling and damages it could cause?

Your assumptions are all correct - This is an issue due to the MAF sensor signal to the ECU registering a certain amount of air that is no longer entering the engine. A MAP-based ECU will eliminate the problem although you'll still have no boost and no power.

The R33 GTR is a little old by modern ECU standards and only incorporates narrowband O2 sensors which are used for closed loop operation. There's no potential to correct the AFR under open loop operation.

Most aftermarket standalone ECUs can incorporate closed loop fuel control and you can also usually set up safe guards against a lean or rich condition if desired.