I wouldn't do this with collapsed subheadings. Instead I would place the subquestions into a rich text Content Control and then hide/show that range according to the answer they give. This code and attached document shows how I've made it so you don't need to edit the code to add more sections - just set up the CC title or tag properties in matching pairs.
Code:
Private Sub Document_ContentControlOnExit(ByVal aCC As ContentControl, Cancel As Boolean)
Dim aCCont As ContentControl
If aCC.Tag = "Has Subquestions" Then
For Each aCCont In ActiveDocument.SelectContentControlsByTitle(aCC.Title & " Subquestions")
aCCont.Range.Font.Hidden = Not aCC.Checked
Next aCCont
End If
End Sub