Whenever any firefighter, after four years of service, shall die from natural causes, or from an injury not sustained in the performance of his or her duty and for which no pension is provided in this chapter, and who has not been retired on account of disability, his widow or her widower, if he or she was his wife or her husband at the time he or she was stricken with his or her last illness, or at the time he or she received the injuries from which he or she died; or if there is no such widow, then his or her child or children shall be entitled to the amount of his or her contributions, plus accrued compounded interest, or the sum of one thousand dollars, whichever sum shall be the greater. In case of death as above stated, before the end of four years of service, an amount based on the proportion of the time of service to four years shall paid such beneficiaries.