Think of how much things changed in the New World between 1500 and 2000. You went from natives seeing a little bit of European activity to all the natives killed or put in reservations, then released and given the crumbs of a special citizenship. You went from the world just getting into gunpowder to the danger that a rogue state could fire nuclear missiles across the ice cap and kill entire cities. People had ships that could barely traverse the ocean to flying to the moon and maintaining a manned space station. Most people were barely literate and communication was at the speedof a horse, to much of the world is connected by radio waves and a sattelite-supported global Internet. One used to be able to buy a book if one were wealthy, to the poorest able to buy 5 used books for an hours' wage and access so many public domain titles that it's physically impossible to read them all in one lifetime.

This on an entire two continents, from the northernmost icy reaches to the almost-arctic south.

That said, advancement is swiftest where advancement has occurred. Human progress has never been faster than it is now, and with some hiccups the progression extends into the past with slower progress found the further back you look.

Take the year 600 AD. Not so much changed in England between 600 and 1100. I mean, things surely did change, but when you compare it to the changes felt from 1500 to 2000 it's like a blip in the cultural spectrum. And just what societal advancements happened in New Guinea between 1,000 BC and 500 BC? Probably virtually nothing.

So I would first off say that the places with the least cultural and technological advancement would change the least in 500 years, and the ones with the greatest cultural and technological level (considering magic here as technology) would advance the fastest.

This would be a good time to start introducing gunpowder. If you do another 500-year leap you can go from black powder and ball to sealed cartridge bullets and automatic weapons and early tanks. The next leap could result in futuristic stuff that works a lot like magic does, like early Star Trek technology. Who knows what the next leap would be - probably more like a weird mecha anime or Firefly.

Anyway, point is you can make a lot change or just a little. But anything that existed before has a solid chance of being gone, replaced by something else, including countries. Only very important buildings that were built of stone and restored every century or so would have a chance of still standing. Ruins would be more poignant to the players since they remembered last weekend this dungeon was a bustling city. Small organizations probably disappeared into the mists of history, or became major social movements. No good way to tell.