No Beneficiary Designation- distribute to estate

[Kat]

I have a 401k plan where the participant died in 1998.  He has a small balance in the plan.  The employer who sponsors the plan has been purchased several times through-out the years and does not have any records going back that far.  The participant has a small balance and we were attempting to do a small balance cash out when we found he was deceased.   There is no beneficiary designation on file with the recordkeeper or the plan sponsor.  We have done searches and have not been able to determine if the participant had any family.  The plan document states to distribute to the estate of the participant.  Our dilemma is that we do not have any information on an estate to distribute to and the check will go uncashed.  The recordkeeper refuses to escheat the balance.  

Does anyone have any guidance they can offer to us?

[FORMER ESQ.]

Does the plan document indicate what happens if the participant's heirs are not located? Does the plan say you can escheat?