The total number may not be higher. But you may have one manufacturer that introduces a bug in a firmware update that kills a huge number of people in one go. The next week they issue an update to fix the problem.
Does it make sense to increase the driver's insurance premium because they (unknowingly) bought a faulty product?
If the insurance market trusts it then yes. This isn't a hard concept. The same lines of reasoning govern planes with autopilot, or even automatic fridges. Insurance + engineering standards = alignment of incentives and economic growth.
so join the manufacturer as a defendent or sue for contribution. Self driving cars would not be the first time in history where a third person was injured by a defective product used by a diffrent person.
You need insurance to be on the road. If you insure your driverless car, then it is insured. End of story.