It is quite an interesting idea. But you have to consider...
1. The Western empire fell in 476, but the the Eastern. Some what do you think about the left behind Byzantine Empire?
2. Inner political system, economy, invasions of barbarians and other matters brought the empire to an end; would they not happen to a republic?
3. The Roman Empire, actually, had doomed for many years though apparently it still existed. That means the goverment was very weak at that time. Would it splited up like Europe nowadays, without a real word "destroyed" - as in fact it was?
4. Imagine if it survived, the history afterwards would be completely different. Perhaps no Feudalism, no Renaissance, no Revolutionary time, no USA ( ), no Napoleon, no imperialism (or yes, maybe), and surely, no WWI, WWII and Cold War. With a world that is totally different, well, I dare not to imagine. Just think about your very own life; you are from USA, right? Perhaps there would be no you?! Or maybe you are in Europe and speak Latin and Greek ? And about me, I am from Hong Kong. Perhaps there would be no Britain to colonize Hong Kong and - ah, very luckily - still a happy city in China , perhaps?
and um...what if there is no World Cup?
Italia cannot win?!?! /__\"