I know that that 'links' dialog doesn't show every possible reference, because it usually doesn't contain anything when in a drawing or assembly which has references to other model documents. However, if something is truly 'unreferenced' I'm not sure how you would break or delete that reference. There are several possible 'types' of references though, and many possible types of objects at the ends of those references.
Here is just one example iLogic rule you can play around with that dabbles with one main possible type of references (OLE).
Dim oDoc As Document = ThisApplication.ActiveDocument
oCount = oDoc.ReferencedOLEFileDescriptors.Count
If oCount = 0 Then
MsgBox("There are no OLE References.", vbInformation, "iLogic")
Exit Sub
End If
For Each oRefOLEFD As ReferencedOLEFileDescriptor In oDoc.ReferencedOLEFileDescriptors
oVis = oRefOLEFD.BrowserVisible
oDName = oRefOLEFD.DisplayName
oEmbedded = IsNothing(oRefOLEFD.FileDescriptor)
oFFN = oRefOLEFD.FullFileName
If oFFN Is vbNullString Then oFFN = ""
oLKFileTime = oRefOLEFD.LastKnownFileTime
If IsNothing(oLKFileTime) Then oLKFileTime = ""
oLogName = oRefOLEFD.LogicalName
oDType = oRefOLEFD.OLEDocumentType
oRefStatus = oRefOLEFD.ReferenceStatus
Dim oData As String = String.Empty
oData = "DisplayName = " & oDName & vbCrLf & _
"FullFileName (Empty If Embedded) = " & oFFN & vbCrLf & _
"OLEDocumentType = " & oDType.ToString & vbCrLf & _
"ReferenceStatus = " & oRefStatus.ToString & vbCrLf & _
"Visible in Browser (if True, seen under 3rdParty folder) = " & oVis & vbCrLf & _
"LogicalName = " & oLogName & vbCrLf & vbCrLf & _
"Do you want to delete this ReferencedOLEFileDescriptor?"
oAns = MsgBox(oData, vbYesNo + vbQuestion, "iLogic")
If oAns = No Then
Continue For
ElseIf oAns = vbYes Then
Try
oRefOLEFD.Delete
Catch oEx As Exception
MsgBox("Failed to delete it." & vbCrLf & _
oEx.Message & vbCrLf & oEx.StackTrace, vbExclamation, "iLogic")
Continue For
End Try
End If
Next
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Wesley Crihfield

(Not an Autodesk Employee)