Thrall isn't Warchief. He goes off and lives in Durotar working as a teacher. We don't hear from him for a good long while, if ever.
The "Warchief" Position is suspended and the members of the Horde work on rebuilding and readjusting their culture to stop repeating this stupid aggressive regression. Particularly the Orcs, which are run by a mix of Shaman and older Warriors like Warlord Krogg. The Blackrock clan members are sent to work in the empty fortresses of Northrend under the watchful eyes of Saurfang, Eitrigg and Ariok, the dragonmaw go along with them to tame protodrakes and release the Magnataur the Horde had captured.
Most of the various Horde ogres are led by Rexxar back to Outland, though a few remain behind on Azeroth. Once there they settle around Hellfire, Blades Edge and Nagrand, relieving a lot of the Horde Forces there, and allowing Nazgrel to come home.
Vol'jin gets a ton of members of other troll tribes as refugees. Though a lot of trolls still want nothing to do with the Darkspear, they're finally at a healthy population level and in a position of political power. Vol'jin works on building homes for the refugees in various parts of the world and rebuilding troll culture. Primal Torntusk runs the Hinterlands.
Baine realizes all this nonsense could've been avoided if he'd had more of a spine, and dedicates the Tauren to tracking down Magatha and killing her before she gets to Expansion Boss levels of power, while also building up after all the losses from the Cataclysm, Quillboar, and Grimtotem. Dialogue with the Yaungol is opened. Roanoak Icemist is approached by the Nerubians but isn't eager to deal with them. The Forsaken courteously offer to take the diplomacy off his hands.
Sylvanas creates an effective border stretching from the Gilnean Wall, to the Thoradin Wall, and Andorhal, and prepares for the long work of turtling against the Alliance for the foreseeable future. The Forsaken realize they have like, four Val'kyr left and begin researching alternatives. Lady Cozwyn serves as Ambassador to the recovering Nerubian Empire.
Lor'themar realizing the blood elves are not going back to the Alliance after the incidents with Theramoore, Darnassus, and Dalaran, works at integrating in the Horde with a meaningful way so they're not always at the fringes and actually have a degree of leverage without the Forsaken. Aethas thinks Rommath was behind all that Dalaran Darnassus stuff, Rommath thinks Aethas is an idealistic loon that forgets most blood elves don't agree with him. Bloodwatcher works with Halduron and Vol'jin on letting some forest trolls live in the ghostlands.
Gallywix died as the rebel armies advanced on Orgrimmar and has been replaced with Sassy Hardwrench as leader of the Bilgewater Cartel, which begins to rake in cash by using its technology to assist in the demilitarizing of the Horde, and selling off the scrap and excess to the Steamwheedle, to help in the retaking and repair of Undermine.
The Houjin go to work helping the Horde aligned Hozen stay out of trouble on Pandaria, and dismantling the Horde Fortresses to create temples or Horde trading posts in their place. Ji Firepaw visits Orgrimmar to teach orphans.
Varian goes home put Taylor in charge for awhile and spends some quality time with Anduin and relaxes for the first time in like ten years. Kul'Tiras and Stromgarde set up trade with Stormwind and Ironforge to start getting back on their feet. The Westfall inn is put out and the area once again becomes a healthy breadbasket. Archbishop Lazaril purges Duskwood of its corruption and establishes a new abbey at Ravenhill to oversee the cleansing of the area alongside the worgen. Reconstruction on the front gate is finished, and work on the Park Districts ruins is started.
Brann partially fixes Magni with help from Lorewalker Cho after seeing the Mogu tech. He's still stone but he can communicate. Moira isn't happy at first but Magni admits he was a jerk to her when she was younger, and agrees to give the Dark Irons an honest chance. Moira's mollified enough to stop being obstructive and they start working out their issues. Slowly. The Dwarves set up a large meeting for all clans, including the Frostborn, and begin piecing together what they know of the Titans and Old Gods to better pepare for further threats.
The Night elves call out Malfurion on his pacifism and Tyrande agrees with the popular opinion after a talk with Jarod Shadowsong. A newly militant attitude takes hold as the resurgent Sisterhood of Elune starts to push the over-exhausted Druidic forces out of the limelight. Night elven borders along Ashenvale and all through desolace and Feralas are strengthened. The Highborne are given a degree of legitimacy and, while still closely watched by the Wardens, are slowly integrated into Night elf society proper. Shandris starts planning an expedition to free Neptulon from the Naga.
The Gnomes reclaim the upper sections of Gnomeragan but realize the lower levels are too irradiated to inhabit any time soon, and so they open the top of the mountain to allow open air access, and build a series of airborne city sections connected by various mechanical devices. They continue working with the Dwarves to reverse engineer titan tech for the Alliance. Gelbin invents a sort of global 'evil' radar to track old gods and demons.
The draenei mostly work on fortifying Outland, and moving civilians/soldiers back and forth from Outland and azeroth using the Exodar. Velen sends a few contingents to felwood and desolace to help clean the places up. He then establishes a great Cathedral in Icecrown to see to the freeing of the souls there while preparing for battle against the Legion.
Genn sets about fortifying the Gilnean wall and planning assaults on Lordaeron with Stormwinds support, while using Gilnean/worgen colonies around the rest of the world to raise the necessary funds to repair all the damage his country has suffered. Krennan aranas works with minds from the rest of the Alliance to develop a blight counteragent. He and Gelbin are pretty darn close to one. Tess Greymane is visiting Stormwind and hanging out with Anduin. Everyone keeps thinking it's romantic, they don't really see it. Crowley and Lorna argue about the blood curse, Ivar keeps being a jerk until Crowley beats him down.
The Tushui work with the Jinyu and Grummle to repair the Serpents Spine and damaged temples in Pandaria, as well as supplement the Shado Pan and Golden Lotus's numbers. Aysa is getting used to her new legs since the old ones got blown off in the siege. Ji rescued her but things are still pretty icy between them since it's possible he was the one that fired it.