In the event the participant dies without a valid beneficiary designation on file, or if no designated beneficiary survives the participant, any balance remaining in the participant’s account shall be payable to the participant’s survivors in the following order:

1. (a) The participant’s spouse.
2. (b) The participant’s natural or adopted children.
3. (c) The participant’s parents.
4. (d) The participant’s brothers and sisters.
5. (e) The participant’s estate.