The rights of any person heretofore or hereafter retired shall continue to be measured and governed by the terms of the system in effect at the time of such retirement and should such person die during continuance of such retirement the right of the spouse, child, or children of such deceased retired person and the rights of the spouse, child, or children of any other deceased person or participant shall be measured and governed by the terms of the system in effect at the time of the death of such deceased person or participant.