I don't think it will win in any court because the virus is everywhere and it's invisible the accuser will have a hard time proving that he really gets the CoVid in the facility, they could have got it in their homes in while travelling while in the market or while in the street it's hard to established the fact on this case but I don't like casinos open at this point of time people should only stay home and restrict their moves.
A lot of countries already managed to pin point the location of a contamination source. It might not be very difficult to prove that a certain place contaminated it's users.
Of course, the gambling casino can be scan for potential virus and if eventually found that any of these gamblers where effected in the casinos, then the lawsuit will be establish. Dangerous spots around certain areas are well known to the agency responsible as hot spot for the virus, and if the gambling casino areas are verify to be dangerous zones for this virus then there will surely be a lawsuit against these Las Vegas gambling casinos.
If due protocols where observed before now there won't be any reason to be scared of any gambler initiating lawsuit against them. Humans lives matters.