I just love that my post became an argument.
Let's go back to the original subject. Now in my speculation and extensive study on this subject seeing as I don't really have a life until I can get my working visa, get a job, get my SATs out of the way and get into college here in New Zealand- I have come to the conclusion that Persians had they one at Thermopylae and a couple other key battles would have probably come to dominate Eastern Europe. I don't know if I said this before but in my own opinion I don't think the linguistic diversity of Europe would've imploded once they did, because Persians don't seem to have pooped on every culture they ever conquered. Elamite and Aramaic actually became official languages of state, and the diverse linguistic picture in Iran today says at least to me that they weren't too into forcing language on others. That being said I think it's possible that an influx of Iranian immigrants into central Europe may have displaced some populations had they conquered the Balkan Peninsula, but I think that the Paleo-Balkan family would still exist today.
The fate of the Anatolian languages is another interesting question, as they were still spoken during the time of Xerxes and it really wasn't until Greeks started immigrating into Anatolia that they started to decline: culminating in Alexander the Great's conquest which pooped on history and left an irremovable stain.
Setting the stones on the road for the Romans, Greeks didn't respect other people and saw all things Greek as superior and imposed their ways on others. So the already dying Anatolian languages just died out because no one cared anymore, just the way they didn't about Elamite because the new fad was Greek with a side of Iranian languages.
So had the Greek civilization been nipped in its infancy, it's possible, but in my personal opinion not very probable that Anatolian languages might exist today. It's possible though.
With Rome, the fact that Latin even survived the period is one of the miracles of history. Rome and the Latins who populated it were a tiny minority who suddenly became important, and their language displaced more important languages in Italy, like Etruscan. So if you actually paint a picture of history that makes sense, instead of what happened, Latin would've gone extinct because it just wasn't important.
So what I have come up with is a bit of a reverse history. In my own opinion, and I am no expert, just a kid with no life at the moment, Achaemenid Persia would probably have enjoyed a prosperous few centuries while controlling an Empire from the Balkans to India. But I think it probably would have fell apart if not before than at least around the time of Christ, just because it was an absolute monarchy without a lot going on for the people, and it would've been spread pretty thin. It's possible that in conquering the Greeks the Persians might have absorbed important ideas though, like the idea that you can't just piss on everyone's heads without the courtesy of calling it rain, typically referred to as democracy.
But I don't doubt that after this split, which could have occurred as early as the death of Xerxes, that successor states with an Iranian nobility would have popped up, just like the Indo-Greek Civilization and the Seleucids.
So the question is what happens in Western Europe? I can see the Etruscans mustering the same might as Rome but I don't really see them taking it as far, or at least if they did come to conquer the Mediterranean, do they poop on everyone in doing so? Or do they just conquer Italy, and other surrounding civilizations pick up on their ideals? Anything's possible I guess, but like I said, I don't think the Etruscans would have forced language on everyone in the same way the Greeks and Romans did.
The Punics are an interesting candidate though, and the idea of them battling with Etruria over the Mediterranean is VERY plausible.
Still, in all these new scenarios, I like to think that Continental Celtic languages and the Paleo-Balkan languages would have survived. Giving rise to a very different picture of Europe.
There would still be aboriginal pre-Indo-European Languages like Etruscan, Basque, and maybe Iberian, or their descendants anyways, and the Celtic Language family would probably be very diverse and cover France, Switzerland, maybe Austria and part of Germany, along with the British Isles and possibly part of Spain. It's also possible that without Rome Galatia might have survived as a state, and would have been able to develop uniquely isolated from the other members of the Celtic family. I don't know though, it's all speculatory.