If memory serves, in the original movie
The Three Hundred Spartans Leonidas gives extactly that order! Thus we get the last charge of the 300.
Whether such an order was actually given, however, we'll never know but such a last defiant gesture does work well into the historical story that we know via Herodotus. So I think it's safe to say it probably was given.
Whether such as a last change would have been successful, well history has say pronounced otherwise. But one never knows as there's always Murphy's Law in such circumstances (even though Ireland was far from known at this point of time).
Now, if Xerxes had been killed at Thermopylae, I think you can kiss good-bye to any further attacks upon Greece at that point in time. If so, then there would be no Battle of Salamis nor the great Greek victory at Plataea.
Consequentially, and detrimental to the Greeks in the end, the Persians may have tried a third time: and this time the Persians win via direct intervention whilst the Athenians & Spartans are slugging it out with each other. Needless to say, the world is very different place as a result...
