Sub CheckIfTOC_Changed()
    Dim rng As Range
    Dim strBefore As String
    Dim strAfter As String
    
    Set rng = ActiveDocument.TablesOfContents(1).Range
    strBefore = rng.Text
    ActiveDocument.TablesOfContents(1).Update
    Set rng = ActiveDocument.TablesOfContents(1).Range
    strAfter = rng.Text
    
    If strBefore = strAfter Then
        MsgBox "No change"
    Else
        MsgBox "Changed"
    End If
    
End Sub