You're right that Sisko ran away on the show when Jadzia died, though to be honest, that's never been a character beat I've really bought. After all, his way of coping when Jennifer died was to continue to do his duty... hard to imagine that in wartime he would just run off, even if it was Jadzia.Oh boy, am I going to get flamed for this, but....
I loved what DRGIII did with Rough Beasts... and onward. Original Sin was not so great, I'll admit that. But I was ok with why he chose to go with the path he decided for Sisko. The man was troubled, always was. I wouldn't be surprised if a lot of PTSD and trauma would be deep in his core if he was every evaluated in real life. According to fight/flight/fright and the almost disturbing attachments of deep love he establishes with those around him, it's not odd that he would choose to leave his family during the turmoil he was going through. It seems Niners are forgetting he did the exact same fucking thing when Jadzia died. So many of his emotional resposnes through out DS9 have always been over the top and intense. And people find it weird that he went to such extremes to do what he felt was right...... Like basically nuking Maquis colonies..... Which happened during the show.
Many of the character traits DRGIII went with for Sisko are all established in the show itself. People just wanted him to be a Godlike superhero after his stay with the Prophets. But no.... He experienced non-linear time for literally both a second AND for eternity. And than became human again. But sure, he's just going to live a normal life know. Going back to Starfleet was an esape. He admitted that. But he also found grounding their afterwards. And as an adult couple capable of communication, something that took a lot of hard work and effort for both of them, he and Kassidy decided that the Robinson was a good place to be as a family.
But fundamentally, the trajectory of Sisko on Deep Space Nine is learning to accept that he is "of Bajor." Of course, you can justify that he might go in a different direction, but this new direction looks back at a seven-year story arc, and basically says, "nah, never mind". Plus, it's fundamentally less interesting than the alternative, which the real cardinal sin here. Maybe it's realistic for Sisko to decide to leave Bajor and captain an exploration ship... but it's also boring. There was never a book that did anything I found interesting with it.
(Plus, I think each line of novels should have its own distinct identity... at this point we have three ongoing novel ranges about married male captains taking care of toddlers!)