On the subject of a long-term departure from the Big Two: Well, we haven't seen anything like the Image Exodus of the 1990's. Only two A-list creators have completely abandoned the Big Two in favor of creator-ownership: Robert Kirkman and Mark Millar. Other than that, you've got some midlisters like Roberson (and Wood, though he acknowledges in that thread that he didn't leave DC so much as they showed him the door).
Now, it DOES bear noting that most of the A-listers working at Marvel right now are also working on creator-owned stuff with other publishers. Now, it could be they'll get the kind of wild success doing it that convinced Kirkman and Millar to jump ship -- but I wouldn't bet on it. Bendis and Loeb have become big wheels in Marvel's TV division, and they're not likely to see anything like that kind of money outside of Marvel. Hickman -- well, Manhattan Projects is all right but there's no way he's making more money from it than Fantastic Four. And Waid -- well, he's playing up his creator-owned stuff and his digital projects in a major way; he'll be the first to jump ship but I don't think it'll happen in 2012.
These guys are doing what Ellis has been doing for the past decade: playing in Marvel's sandbox, and using the money they make there to support their creator-owned stuff.
That and there's a bit of a loop at work here, a sort of progression: you start out doing creator-owned work; if you're successful, you get something at Vertigo. From there you go to DC, and from there to Marvel. And from there, you go back to creator-owned.
The Big Two aren't going to run out of guys who want to write or draw Batman or Spider-Man. There's always going to be somebody waiting in the wings. Once in awhile it'll be somebody pretty damn good.
I really do think we're on the verge of something of a creator-owned renaissance -- Dark Horse and Image are putting out their best books in 20 years, no lie. And it's great news for people who want to wriggle out from under the Big Two -- from what I've heard, even Vertigo's "creator-owned" terms are actually pretty predatory. And they're better than DC Proper, which in turn is better than Marvel. (Which is better than Archie, which is pretty much pure evil, but is still better than Bluewater, which from what I've heard doesn't even pay its creators and instead hoodwinks them into thinking that churning out celebrity comics for Bluewater will get them exposure.)
But still, I think it's great news for everybody from Kate Beaton on up to Brian Bendis. The future of comics IS wide open; I don't see DC and Marvel going anywhere or suffering any major brain drain, but more and more people in the industry are realizing they're not the only game in town. And that's without getting into all the talented amateurs raising money on Kickstarter.