If you don’t retain some kind of actual ownership, they will not be allowed to use terms like “buy” or “purchase” on the store page button. I hope there aren’t huge holes in this that allow bad actors to get around it, but I certainly loathe the fact that there’s no real way to buy a movie or TV show digitally. Not really.
EDIT: On re-reading it, there may be huge holes in it. Like if they just “clearly tell you” how little you’re getting when you buy it, they can still say “buy” and “purchase”.
On the basis of technicality, it will depend very wildly on the ToC of said intellectual property. As you said, GOG just distributes the installer and that is it, the IP holder can technically revoke your/GOG license if that is in the ToC somewhere.
So what if they did? Are they going to give me a court summons to destroy my copy and all of my backups of the game? I don’t think so.