So thanks to not having signed in for a couple months, I actually still had notifications from the last time I chatted about this, and here’s the information someone else found when they looked into it.
In summary, this “policy” is at best someone (maybe even GabeN) stating back in 2009 and 2013 that games will still be (somehow) made available to customers if Steam shuts down.
As far as I know (please correct me if I’m wrong), there’s nothing in the Steam Subscriber Agreement that obligates Steam/Valve to do it. And even if there were, there’s nothing saying they can’t just update the SSA to remove such a term.
Furthermore, even if Valve wants to do this if Steam ever shuts down, considering Steam’s size I’d say it’s less likely to be shut down and more likely to just get sold off if Valve ever does become insolvent, and the new owner of Steam can’t be held to this promise anyway.
So, while it’d definitely be good if this were the case, this seems to be more wishful than written-in-stone.