We discussed the issue of Sisko leaving with DRG III on startrek.com. He made a good case for why Sisko left. I hated that move passionately when I read the book but his reasoning made sense to me. Someone even asked him, "Did Sisko take his baseball or leave it at home?" DRG had no answer; if he left it, that means he wants to come back. Let's also not forget that Sisko only desired to go back to work and had no intention of completely abandoning his family; he was hoping that by working off planet, he could protect them by lack of physical proximity. It was Cassidy who threw him out. She was the aggressor in the break-up. I do wonder what Avery Brooks would think about "Rough Beasts", though.
So that's where he is hanging out now.
There was a similar discussion here on Sisko's behaviour with in Rough Beasts.
He wasn't very keen on the reaction to it around here, the fact that what he wrote and what he intended to write seemed two different things and he wasn't overly keen on the attitude towards him in that thread so he picked his toys up, said he wasn't going to play anymore with us and left in a huff.
Anyway, on the idea of Sisko being the Captain of the Enterprise once Picard leaves is a totally rubbish idea. I personally don't want someone parashooted in from another series to fill the void. Either have Worf get promoted to CO or have a brand new character take up the role.