Any firefighter who has served more than fifteen years and sustains a disability not in the performance of his or her duty which renders him or her unable to continue his or her service, shall within sixty days exercise his or her choice either to receive his or her contribution to the fund, plus earned interest compounded semiannually, or be retired and paid a monthly pension based on the factor of his or her age shown in RCW
41.16.080, times his or her average monthly salary as a member of the fire department of his or her municipality at the date of his or her retirement, times the number of years of service rendered at the time he or she sustained such disability. If such firefighter shall die leaving surviving him a wife or surviving her a husband, or child or children, then such wife or husband, or if he leaves no wife or she leaves no husband, then his or her child or children shall receive the sum of his or her contributions, plus accumulated compound interest, and such payment shall be reduced in the amount of the payments made to deceased.