And it is only really a promise they can keep for their own games. Like I said in another comment, lots of game studios already ship their games without DRM.
If Valve goes under, the games that are gonna be a problem are the ones from the likes of Ubisoft and EA.
They wouldn’t lift a finger to make sure people who bought their games on steam could keep playing them if steam disappeared
In fact they’ve been taking their games back even while steam is still around. Lots of people own unplayable games on steam because the publisher screwed the servers or something.