Dear John Philip Clive,
thanks for an inspiring essay! 'Damasio's patient' is indeed an interesting case telling us something about how we make decisions. I believe, however, that there is some (widespread) confusion regarding the meaning of 'rational'.
To begin with, most pre-modern cultures see the heart as the seat of Vernunft, ratio or reason. Then there are three body areas involved in leading our lives.
a) the stomach - emotion
b) the heart - reason, understanding, comprehension, sound judgement, etc.
c) the brain - logic, intellect, smartness, etc.
Now, neurologically speaking, emotion and intellect seem to be associated with the frontal lobe. The core of intellect though is not reason, but logic. Logic has nothing to do with reason. Already 20th century Vernunftkritik (criticism of reason) factually attacked logic (e.g. technologisation) while calling it reason. But reason (following Kant: die Vernunft geht nie auf die Dinge...) doesn't deal with things or processes, but with invariant principles. Reason is thus a-temporal, though ironically located in the temporal lobe. The frontal lobe is a late development and is believed to process emotion and intellect. This makes sense inasmuch logic deals with temporal if-then constructions, which, as you rightly say, have no singular objective solution and are thus decided by emotion. Hence the collocation of logic and emotion in the frontal lobe makes much sense. Maybe this is why Damasio's patient was absolutely reasonable in recognizing the world, his own situation, photos, etc., but unable to make logical=temporal=procedural decisions.
Reason is a censorial not a creative function, letting pass what is reasonable and blocking everything else. Since logical decisions inevitably open up an unknowable future, the impairment of Damasio's patient to deal with logic may well have made him the most rational man on Earth.
good luck for your essay,
Heinz