Is the injury of an employee, sustained while going to perform prayer during official working hours, which led to permanent partial disability, considered a work-related injury? And what is the Shar'i ruling on insurance coverage for treatment costs, salary, and compensation for the disability?

If a worshipper is afflicted with an illness during working hours, it is considered a work-related injury for which they are entitled to the same benefits as someone injured at work. As for insurance, only cooperative insurance is permissible; any other type is forbidden. If it is not cooperative insurance, then you are not permitted to take more than what you paid to the insurance company.