I think he fights Thurman if Floyd doesn't choose him. I could see a Khan/Swift rematch, but I personally have no interest in it.
I'm of the opinion that Khan is going to hold off on fighting Brook. Not because he's or anything like that, because I don't think he's chicken. An egotistical idiot? Yes. Chicken? No. I just think he's going to hold off on fighting Brook, because there's really no need to rush it. That fight will always be on the table for Khan. And I think he knows that. Really Kell is the one rushing it, because he's trying to strike while the iron's hot for fear of losing and missing out on his biggest payday (much like Khan has been doing with Mayweather). I think Khan will finally decide to fight Brook after he's exhausted every other option available. Just my opinion of course