Not every rollover crash will result in a lawsuit. Some are caused purely by driver error and no one is to blame but the driver. However, many rollover accidents are caused by auto defects, and those usually result in legal action.
If your rollover accident was caused by a dangerously designed automobile, then you can sue the manufacturer of that automobile.
Here's how it works. Automakers are required to sell vehicles that can perform reasonably well under ordinary driving conditions. For instance, it is presumable that a driver may have to swerve around some obstruction in the road. Thus, we should all expect that the cars we buy are able to facilitate that kind of normal, real-world driving maneuver without rolling over. What a car can do in a government crash test is fine, but what we really care about is whether it performs the way it should in real life.
Unfortunately, the reality is that some cars on the market cannot handle such maneuvers. The driver attempts to swerve around a stalled vehicle in the roadway or a deer, and the next thing they know, a chain of events has been set into motion that they cannot recover from.
Vehicles that perform this way are regarded as unreasonably dangerous, and the manufacturer can be sued for selling an underperforming vehicle that then hurt its occupants.
In conclusion, the big question that needs to be answered, in any rollover accident, is whether it was caused by a defect or purely by driver error. If a defect is to blame, then you can sue the company that made the car.