I'd like to match the element that have children and the attribute
  this="true" or the parent of the element having the attribute
  this="true" that does not have children.

match="*[* and @this='true'] | *[*[not(*) and @this='true']]"

I interpreted "children" to mean child elements, if you include child
text nodes, replace  the * inside the predicates with node().

David

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