You want decay in your game? Require an online connection.

To me, it feels weird that games aren’t subject to the ravages of time but real life is; apparently to Randall Munroe it’s the other way around.

If you want to go back to an old game world and see simulated change and decay, you can always revisit a neglected Animal Crossing town.

For real decay, check out multiplayer servers for old online games. It’s like a memento mori for games with kludged-in online/multiplayer requirements.