FFIX and X both do this quite well by simply letting you back into the places that have been struck by disaster. Kilika after Sin, or Alexandria after Bahamut.

It's nice to see people working on rebuilding as well. That's a sure way to hammer home the effect of the diaster. Not letting you explore Insomnia before the World of Ruin was a big mistake in my eyes. You had no sense of contrast. It was shocking to see Alexandria/Kilika in ruins because I'd seen them before the disasters. Insomnia may as well have been just another dungeon.