I've been thinking about a campaign where humans have vanished, leaving behind their crumbling cities. Infrastructure has collapsed without humanity. Some are glad, as the forests have returned to their old glory
Others feel that the world has plunged into a dark age without the human drive and sheer numbers pushing things forward. The non-human races have pretty much retreated into their own communities. Adventurers, being an exception, are travelling into dangerous locales, looting the abandoned cities for wealth or knowledge, while others might seek to discover what caused the loss of humanity. Are there still pockets of humans left somewhere in the world? Can they be returned?
Half-elves and half-orcs would still pop up in orc and elf populations, being either reverered, hated or even sought after in hopes they might hold the key to humanity's fate and possible return.
I think it might be interesting to run a world where humans have gone extinct, and think about how the other races would react. I kind of had this image of hobgoblins starting to fill in the niche humans left open. They'd be very organized, highly militaristic, not pleasant, to live under, but they'd keep the monsters at bay and as long as you paid the expected dues, things might be okay. Anyway, hobgoblin numbers are growing, spreading, building, which could be a good reason to want humans back, especially if some folk are looking back at humans in a golden light.