What happens to a game when the servers go off
Some games stop existing when a company decides they should. Which ones are vulnerable comes down to a single question: how much of the game lives on someone else's computer?

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A film on a shelf stays watchable. A game can become permanently unplayable because a server was switched off, and no copy you own will change that. The difference is where the game actually runs.
Four levels of exposure
Fully offline. Everything runs on your machine. These survive indefinitely, subject only to operating systems moving on — and that's usually solvable with compatibility layers.
Offline with an activation check. Playable locally, but needs to phone home at least once. Vulnerable if the activation server closes, though publishers have often released patches removing the check when winding a service down. Often, not always.
Online components on top of a local game. Multiplayer, leaderboards, cloud saves. The single-player game survives; the rest goes. A partial loss, and usually the acceptable case.
Server-dependent by design. The game world lives on the company's infrastructure. When it shuts down, the game is gone — not degraded, gone. Persistent online worlds, live-service titles and anything streamed rather than installed.
The useful question when buying something you expect to keep: if this company disappeared tomorrow, would the disc or download still do anything?
Why shutdowns happen
Rarely malice. Servers cost money to run, and a game with a small remaining population stops justifying the expense. Licensed music and sports content expires. Platform holders retire old online infrastructure. Studios close.
The pattern is fairly consistent: an announcement some months ahead, sales stopped, then a final date. The gap is usually long enough to finish what you're partway through if you notice.
What actually survives
Local saves, as files on your drive — though without the game they're just data.
Single-player content in games where it doesn't depend on a server.
Community servers, where a game supported self-hosting or where source code was released. Some titles have outlived their official servers by a decade this way. This is entirely dependent on the original design, which is why self-hosting support is worth noticing as a feature.
Documentation. When the game itself can't be preserved, recordings, screenshots and written accounts are what remains. Institutional archives and preservation projects do serious work here, and it's often all that's left of a shut-down online world.
If you care about keeping something
- Prefer offline-capable versions for anything you want in ten years. Check whether it needs a connection to launch.
- Back up local saves. Trivial, and the thing people regret skipping.
- Note whether self-hosting is supported. The strongest predictor of long-term survival for a multiplayer game.
- Act on shutdown notices. The window is finite. If there's something you wanted to see, that's the time.
- Treat subscription catalogues as access, not ownership. If a specific game matters to you long-term, buy that one outright.
The honest framing
Subscriptions and online services are a good deal for breadth and a poor deal for permanence. That's the trade, and it's a reasonable one as long as you know which side of it you're on.
Use them to play widely and cheaply. For the handful of games you expect to still care about in a decade, own an offline-capable copy. Those are different purchases serving different purposes, and conflating them is how people lose things.