I am not aware of any case in which the game was removed from Steam and made unavailable to those who purchased it.
I have several games in my Steam library where they stopped offering for sale and I can still download and play.
I also have one game I can download but not play since the publisher took the backend servers offline. Steam is still hosting the installer.
Physical games or a model like Gog ensure you will be able to play the games in the future. Digital games where you can't transfer the offline installer to any platform you want is trading convenience today for a guarantee you will buy or pirate it in the future.
For those that buy games on Gog, what has been your strategy for backing up the installers? It seems they only make the last few patches available for download. Do you download every patch, or just the installers?
They could be acquired or go under just as well and I doubt that most people are keeping backups of all the installers.
But unlike a disc or cartridge you can have it backed up in multiple places, more similar to family photos.
Also, fundamentally the issue of copyright is a government enforced artificial monopoly. It's ultimately up to to the governments whether you can "own" any digital media in the future. Hypothetically, the governments could come to take your physical media, and the only thing you can do to defend your rights is with arms, hence the US's fixation on their Second Amendment.
Of the two, which is a greater impact? I know of many games with bugs, some even showstopping ones and can't think of any game that I want to play "as released" because the patch makes things worse.
Speedrunners, for instance, often prefer very specific releases of games, because they rely on glitches that have since been fixed.
Sometimes the latest rev a dev shipped before falling off the planet has game-changing behaviors, like stripping all the licensed music because you lost the license.