This concept appears to work IF a heading is the trigger for each block of pages (ie a paragraph which has an outline level other than body text).
Code:
Sub RandomSortOfChap()
Dim aPar As Paragraph
'Add random numbers on headings
For Each aPar In ActiveDocument.Paragraphs
If aPar.Range.ParagraphFormat.OutlineLevel <> wdOutlineLevelBodyText Then
aPar.Range.InsertBefore Left(Rnd(1) * 100000, 4) & vbTab
End If
Next aPar
'Now sort based on the random number
ActiveWindow.ActivePane.View.Type = wdOutlineView
ActiveWindow.View.ShowHeading 5 'show five levels of headings
Selection.Sort FieldNumber:="Paragraphs", SortFieldType:=wdSortFieldAlphanumeric
ActiveWindow.ActivePane.View.Type = wdPrintView
'And remove the numbers
ActiveDocument.Range.Select
WordBasic.ToolsBulletsNumbers Replace:=0, Type:=1, Remove:=1
End Sub