Whereas it is always a pleasure to welcome new posters to the site, you may disappointed by response to your 'what if' post.
Evaluating - indeed discerning - the full truths of known History of times in past and indeed of History being made, is hard enough for most of us. My speculation along the lines of 'what if,' would be a tad ignorant and frivolous - although I happen to be reasonably au fait with the period you suggest. Circa Darius, Xerxes I think you mean?
i hope, however you might be tempted to respond to our sort of posts - engaging in discussion can be interesting too.