It's already happened in at least one case. A light motorcycle ran into the side of a Cruise Bolt a couple years ago, and the police ruled the bike operator at fault. The suit was filed based on the idea that an AV doesn't behave like a San Francisco driver, that is, driving like blind drunk teenager who's in a hurry. The AV Bolt was obeying the law, the MC was not. I will admit to not knowing the outcome, but 'somehow' it made it to the national media outlets. This is usually because a legal firm sent out press releases. A minor traffic accident is not national news.
OPPSS! International news, not national. Here is one of hundreds of articles about it:
GM sued over self-driving car crash with motorcyclist