Unless we get a "too big to turn down" offer for someone, I think there's only really 5 names in the conversation - Lyle, Cafu, Colback, Mighten, and Mbe Soh.Cooper has said that there will most likely be a few outgoings too.
If I had to guess, I'd say maybe Lyle Taylor and possibly Cafu?
Lyle seems like the obvious one to be allowed to leave - we let him go to Birmingham because he wanted more game time, so presumably the same situation applies now we're at a higher level and with more competition for places.
Alex Mighten really needs to go out on loan, a season where he's playing every week like Brennan had at Lincoln would massively help him develop. That also applies for Mbe Soh, but I'm not sure that we can risk letting him go out unless we sign another CB first.
I seem to be in the minority on this, but I think Cafu stays because he can cover a few roles even if he's at best 3rd choice for any of them, and seems to be able to come in after not playing for ages and still be at 100% while maintaining a good attitude about his lack of minutes. Likewise Colback, at least until January when hopefully Richards is back and fully fit.