Plus, if Behr didn't want him back- wouldn't that have just been for the end of the series? For those last episodes? If he had meant permanently years in DS9s future, I don't think it would have been written telling Kasidy he would be make, albeit at a vague time.
In the original script, Sisko was permanently with the Prophets, effectively dead. Avery Brooks insisted on having it rewritten so that Sisko would promise to come back, because in his mind the original ending struck too close to home with regard to the widespread present-day problem of African-American men abandoning their families. To him, Sisko's loving commitment to his family made the character a valuable role model, and he didn't want an ending that undermined that by having him leave his family forever.
Still, I think it's reaching to assume from that fact that Behr wanted Sisko to be gone forever and that any departure from that is somehow compromising his "vision," as a couple of posters here seem to be suggesting. Behr may have run the show, but he developed the series in collaboration with multiple other people, and frankly they were making a lot of it up as they went along. It's not like there was some predetermined plan for how the whole thing was "supposed" to go -- let alone for what was "supposed" to happen after the show ended. Heck, if they'd given any thought to what would happen after the finale, they wouldn't have left so many huge dangling loose ends.