I always felt Shelby's remark implied that the fleet "assigned to this region" would be back up... The loss of thirty-nine ships, while terrible, seemed relatively small for it to be a substantial number of vessels in Starfleet's entire fleet in the late 24th century. The Federation is made up of well over 100 planets (150 by INS, IIRC) by then. DS9's DW stories seemd to be much more realistic in its numbers.
As for the promotion questions, I remember reading a rumor that Stewart was renegotiating his contract and that if he pushed too hard during the summer hiatus, Locutus would die, Riker would remain captain, and Shelby would be added to the cast as XO. I later read that this was BS but I always enjoyed that rumor wondering how the dynamics of the show would've changed if that had occurred. I also liked the (false) rumor that accompanied the episode "Second Chances" in which Riker's transporter created double is found - Cmdr. Will Riker would get promoted and leave while Lt. Tom Riker would stay on the show. A new character but not really. Lots of possibilities!