What does the plan say? Our VS document has the following:
However, if a missing Participant or Beneficiary has not been located by the time the Plan terminates, the forfeiture of such Participant’s or Beneficiary’s distributable amount will be irrevocable.
I assume you're referring to 403(b)s in the private sector? A public school is pretty much stuck with 403(b) or 457(b), unless there is a grandfathered 401(k).