1) A game engine (code, that usually runs on end-user's device). This can be preserved / run / reverse engineered / re-written / bugfixed etc for all eternity as long as anyone cares. On original hardware or emulators.
2) Data: maps, graphics, sounds, etc. Same as 1) but (mostly) platform independent.
3) Online services like game servers that connect players online, maintain the state of a shared 'world', player stats etc.
Games of old don't have 3), so that's just a matter of preserving code & data.
Later games have 3) without depending on it. Bonus points if 3) can be provided by 3rd party like players hosting their own game server.
For such games, "purchase" means exactly that (or at least it should).
Some % of recent games depend on 3) to the point that game becomes worthless if vendor pulls the plug. With no option to have 3rd party run a game server.
Such games are better regarded as "online service", and lend themselves more to a subscription model imho. With the understanding that service (and thus, the game) will disappear at some point.
Developing a game can cost serious $$. But running server(s)? Easily covered as long as there's a paying userbase. So it's beyond me why a vendor would pull the plug as long as paying userbase exists.
People still play very old games in emulators. You can find WoW servers not operated by blizzard. While current copyright law might allow companies to sue them to oblivion I do not see why we should just accept this as the reasonable standard.
Maybe it is a sign that we should update copyright law. If the publisher does not want to maintain a game anymore why should fans not be allowed to operate their own servers?
The basis of copyright is that, once the terms of copyright run out, the work then belongs to the public. Preventing preservation is effectively theft in a way that almost no other copyright infringement can be equated to.
Rights holders who impede preservation and steal works from the public should effectively lose the right to hold copyright in the first place. You shouldn't get the protection if you're not willing to ensure you hold up your end of the bargain when it comes time to give it to the public.