Is this even a legitimate case to sue the band? Bands do have some say when it comes to their shows but a majority of the time it's the concert promoters and managers that determine stuff. LiveNation pushed to have the show continue despite the weather so as far as I'm concerned these people should be filing the lawsuit primarily against LiveNation and not include the band. I don't fault the band for what happened.
If I remember correctly the stage collapsed at a Cheap Trick concert this year, too. People didn't go out and sue the band because the stage collapsed.
I have been to concerts in bad weather before and it says on your ticket the show will happen rain or shine and it also has a liability statement from the concert promoter on the ticket. When I saw Korn back in 2003 it was raining with lightning all day and night and they still held the show. It depends on what you feel safe with, imo. If it's raining or looks like a tornado outside and you don't feel safe then leave. I would rather be out $30 and miss a show than be unsafe and potentially die but hey... to each their own.