Today's Pitchfork headline: http://www.pitchforkmedia.com/news/44318-kim-gordon-thurston-moore-separate/
I don't really know what to make of this. Obviously on a personal level I'm sorry for them. From a band level, it's hard to say what will happen. Obviously 93% of Sonic Youth fans would just like Kim to leave and to have them continue on with Thurston, Lee, Steve, and Mark Ibold. That would be an unspeakably awesome band. But more likely will be the decision that there is no Sonic Youth without Thurston or Kim (or Lee or Steve, you could also argue) and they will thus break up. That would suck.
I suppose they could also continue their professional relationship and keep things more or less status quo, although their press release was far from assuring in that regard.
Relationship aside, I'll say this: From Murray Street through The Eternal, Sonic Youth has been on what's easily the best run of their career, and in the past decade, they've gone from being only an occasional listen for me to one of my favorite active rock bands. It would suck if this spells the end of that run.