The battle of Thermopylae is traditionally stated to have lasted at least a couple of days. Let's say that the Persians, unbeknownst to the Greeks already had knowledge of the goat path. The Persians surround and slaughter the Greeks within a day's time with minimal losses relative to OTL. What effect, if any does this have on Xerxes' invasion, along with the modern image of the Spartan last stand at Thermopylae. This scenario involves all 7,000 or so Greeks getting surrounded and slaughtered/captured.