bluethief: On GOG and Steam, whenever a game's delisted, it stays on your library if you have purchased it previously. I don't know of a case where it was also removed from the library if not by mistake.
But yet, both GOG and Steam have no problem with removing and/or altering content from games that are already in the customers' libraries on their platforms (as they are about to do with Alan Wake, and as they have also done with many other games before that), and no longer providing any access to the unbutchered/unaltered version.
One could reasonably argue that by removing and/or altering a game's content, those stores are actually removing the game, and then replacing it with a
different game.
Removing the
game itself isn't much of a further leap from that; it's very close to what they have already done and continue to do on a regular basis.
I wouldn't be surprised at all if Steam and/or GOG start removing games themselves from customers' libraries.
The only thing I can think of that might possibly stop them from doing that would be worries over lawsuits. But they had no reason to worry about lawsuits regarding butchering and/or altering content, so probably IMO they might feel that they have no reason to worry about removing games themselves either.