What is the ruling on demanding compensation from the insurance company for the electrocution of a cousin at work, given that the employer is covering the medical expenses and his injury is still ongoing?

If the insurance is cooperative, your cousin is permitted to receive the insurance amount. However, if it is commercial and optional, then subscribing to it is not permissible. If the company compels your cousin to subscribe to commercial insurance, there is no sin upon him, but he is not allowed to take more than he paid or what the company paid. If his injury was due to a crime committed by another, then the perpetrator must pay the "arsh" (compensation) for his crime, and it is permissible to take it from the insurance entity. This does not contradict the landowner covering his treatment expenses.