I believe the worst risk for seats is the slide-rails breaking or separating from the seat. I suppose that and the back of the seat breaking.

Ralph Nader in his book “Small--on safety: The designed-in dangers of the Volkswagen” describes how the driver and front passenger seat could fail in a rear end collision. Drivers were paralyzed when the seat separated from the rail throwing the person against the slanting rear roof causing a broken neck. Certainly the old 1960’s Beetle was an unsafe vehicle, but the faulty seat rails added to the danger.