Obviously, the key element of a lawsuit would be proof that the nursing home disobeyed state or federal guidelines regarding social distancing, self-quarantine or PPE utilization/ hand hygiene recommendations. I think this could be hard to do, given the severe fluctuations in federal attitude during the days when exposure risk turned out to be higher than most people thought. Unless the home brazenly ignored basic standards. Because at the end of the day, it is a balancing act, if insufficient staff came to work due to over-zealous policies, some of the patients would likely have died, too.
If you haven’t read them, the articles describing the New Orleans discussions about Mardi Gras planning against the Covid outbreak are pretty interesting. Their assessment of their risk kept evolving, but not at a rate that was sufficient to plan appropriately.