So a game idea got described to me and I thought it sounded interesting.
It's a game where you play an elf, specifically, The Last Elf. Anything human-like is extinct including elfdom, and humanity is essentially fading out of existence, essentially wiped out by an invading race of goblins or beastmen.
It's a revenge driven game, you're not really trying to save anyone or anything. It takes place in an open world on a single continent with a detailed ecosystem, there's cities populated by the invaders, supplied with various resources to function. Day night cycle, they wake up and go to work on their what have you. There's plenty of nice and serene areas too, but they get slowly encroached on as the enemy urbanizes.
So your real goal is to wipe out the invaders and their entire emergent civilization through any means; destroying food supplies, spreading disease, inciting wars among factions/city-states, killing sprees, etc.
Regarding the you as elf fighting things, it'd probably make sense as a third-person thing to emphasize being mobile in addition to some pretty difficult combat. Standard access to a variety of weapons, traps, magic that is powered by the blood of your enemies.
There'd be a counter in a menu or even constantly on the hud telling you how many invaders are left in the world. For the longer reaching plans that the player enacts, they can choose to wait a few years, but they'd reproduce and advance technologically. Wait too long without doing anything to them, they reach a renaissance and you lose. But wait a long time and they forget you were real, and form legends and so on.
So when you wipe them out, you can continue playing as normal. Or you can idle for a few minutes, and the character starts walking back to where the game started, and says it's over. Then you can start a new game.
I doubt any large company would try something simulator, and anything that actually gets made would probably be heavily abstracted and lose a bit of flavor in the process. But a wish is a wish.