Well, CEO Newell said it and that's still not enough for you, although i agree with you they are in their right not to do it. Though, pissing off millions of customers ain't exactly the best thing to do. Sony made that mistake with the PS3 and got pwnd by the hackers. The EULA is just a cover-ass for legal stuff, sure they can use it where they see fit but that won't make a good name for them. That's why they have support, try to help those with problems. Treat your customers good and they tread you back the same way.
can Valve unilatterally disable the DRM for all games that rely on their DRM with no notice? --> this no one knows, but probably when the publisher struck the deal with valve they informed him what would happen if they go bankrupt.
Though how would the Steam client tell the difference between the servers being shut down due to them going out, compared to any other reason that servers can be down for? --> ask valve not me, i don't work for them
Someone buying them sounds logical to me too, but right now they must be really stupid to sell it. It's simply a goldmine for profit.
As for the "what if's", right now nobody should worry about steam going down, somewhere i read they made 200% income from selling stuff and accumulated 30 millions of users so that ain't a small feat.