That’s a good question, and we might see the courts sort it out on this one, depending on whether the victim’s family sues.
Tesla has been vocal in the past that they are not liable for Autopilot failures, since it is merely a driver assistance feature. But just because they say that doesn’t mean the courts will see it that way.
On the other hand, Google and Volvo have said they will accept liability for any accidents resulting from their self-driving cars. But neither Google nor Volvo has offered those cars to the public yet.