I suspect that a crash serious enough to damage the unibody would be a write-off with or without it. In modern cars, mere deployment of airbags is stupidly exp

I suspect that a crash serious enough to damage the unibody would be a write-off with or without it. In modern cars, mere deployment of airbags is stupidly expensive, and almost a write-off on its own. You need to replace not just the airbags and seatbelts, but also seats and all interior parts that they've exploded (and airbags are everywhere now).