How obtuse is the following interpretation?
When you make a purchase on Steam, you are paying Valve to grant you access to a game. You are not paying for the game itself, and you do not gain any sort of ownership over its contents. If Steam goes under, then its ability to continue providing you access to the game is compromised, which means that (excluding the offline access alternative) you simply cannot play it anymore. There is no, "b-b-b-b-but, I own the game" because you never bought the game in the first place.
It was just a happy side effect of an aging content delivery model that we can continue playing our old carts and disks long after publishers and platform support have evaporated.