But why - in the event of their demise - wouldn't Valve simply release a patch to enable regular-old-no-Steam-needed gameplay? If they're gonna close shop and the game is to become abandonware anyway, why would they care about the Steam authentication anymore? Seems to me like they'd just make one final patch that turns it on permanently.
I'm sure when Valve does go down (eventually. Maybe 20 years or so) Gabe will push that big red button under his desk that unlocks HL2 from steam (which they already have, btw), and detonates that nuclear reactor they have under their building.