They were a worker's compensation subscriber.

Worker's comp doesn't aways prevent liability of the employer. If Gross negligence is proved, the employer is liable even with worker's comp. Also, depending on how he passed away, there could be a claim against a 3rd party even if the employer had worker's comp.

Also, not all plans qualify as worker's comp claims. Some employers make it look like its worker's comp when it's just an imitation worker's comp claim.