New interim Starfleet CO arrives to take command of the area, new OPS officer and Strat-Ops officer as well... Episode deals with the change of command, and leads into a three part episode where everyone has to adjust to his/her/its style of command while he/she/it gets a crash-course in the local politic and overall situation. Then I'd do a couple one off adventures so we can get to know the new crew, then start building a new story arc.
I don't. No new COs. Kira should remain the commander of DS9. Give her a Starfleet XO and a few other new officers. And bring Ro Laren to DS9 as the new Chief of Security... Hey, wait, that's exactly what they did in the novels.
Though Sisko, O'Brien, Odo and Worf are gone I'd only bring in two permanent replacements, an XO for the station leaving Kira in command and another Bajoran to take over security. I'd like that to be a Bajoran who has appeared before in DS9. I wouldn't bring in Ro though like the novel, never a fan of hers. Nog would become a regular taking on the engineering duties of O'Brien. I'd also promote Kasidy to a regular giving her a priority role in Bajoran politics and religion based on her as the wife or the Emissary and carrying his son, gaining more influence with the disappearance of Winn with restricted evil material. As for Sisko I might save him for an appearance later in the season. Garak might make an appearance to tie in some info with post-war Cardassia. As what would happen I'd wouldn't have Bajor join in the first episode, maybe make them reluctant to join the Federation out of fears that they would be screwed by the Federation suffering the post-war blues. Maybe a plot with the True Way attempting to blow up the station and destroy the wormhole. Oh, and Ezri would die in the first two minutes after tripping over a bomb and setting it off.