Maybe countersue for unnecessary anxiety or something like that. Especially if any of the passengers already had other issues such as previous heart problems (fear could cause an attack) or if someone was already nervous about flying in general. I am sure there are all sorts of things that could be brought up.
The passengers can sue for violation of their RIGHT OF FREE SPEECH and also RIGHT TO SELF DEFENSE !
There is some sort of law (cannot recall it's name) which protects people from retaliatory lawsuits if they are complaining to government authorities. Presumably that would include the airplane captain and his staff.
IIRC it even includes provisions for punitive damages.