According what I heard this morning, the case was never closed and that there always was an FBI agent and a NYPD detective assigned to the case though I can only believe the actual investigation was actively followed all through these past several decades.
Also, it seems the family of the missing school child never moved from their apartment and in fact never changed their phone number since the disappearance.
If they do find the body or evidence of the crime, then the case will come to an active murder case and the family will have a long time before closure comes about. Either way if the body is found or not, this reminder for the family will be a difficult thing. Quite sad indeed.