Is the end-of-service bonus stipulated in man-made laws binding on the employer according to Sharia, if it was not agreed upon between the employee and the employer?

If the employment contract does not stipulate the employee's entitlement to an end-of-service bonus, then reference should be made to custom or the law governing the relationship between employees and employers. If the law stipulates the employee's entitlement to this bonus, then the company is obligated to pay it to him.