Jaina - I think the Horde and Alliance will end up trying to make peace, but Jaina is still a nutjob and becomes a liability, sabotaging the peace between the Alliance and Horde. She frames the Alliance for attacks against Horde settlements, and the war begins again until it is discovered Jaina is responsible. (Insert raid) Instead of being executed, Vol'jin insists that she is just imprisoned, and that somewhere inside is the Jaina that once was.
Vol'jin - Vol'jin struggles to handle his disillusioned Orc troops, whose race faces persecution after the actions of Garrosh in SoO and Draenor. Becoming hated in the very Horde they created, the Orcs become a minority and it falls to their non-Orc Warchief to inspire them once again.
Saurfang - Saurfang becomes the racial leader of the Orcs, appointed by Vol'jin to try and boost morale. He tries to inspire them the best way he knows how- by standing with them on the frontlines. He teaches the Orcs that they have the blood of shamans and warriors in them, and that they must honour the dead and the living, and take life only when needed.
Garrosh/Thrall/Zaela - On Draenor, Garrosh is killed by Grom when he tries to renegotiate a pact with Kil'jaeden when the other warlords fall. Garrosh tries to stop him, but fails, just as Thrall arrives to reveal who Garrosh actually was. He leaves behind a child whom he had with Zaela while on Draenor. Zaela gives her son to Thrall, saying that after what she has done she could never raise a child, and decides to stay behind on Draenor. Thrall returns to Azeroth with Garrosh's son, and promises to raise the child alongside his own, as if they were both his own blood. He hopes that someday the two might become brothers in a way he and Garrosh never could. He calls Garrosh's son 'Gromgar', as he went unnamed by his neglecting parents.
Sylvanas - With peace between the Alliance and Horde pretty much obtained, there is little conflict. Less conflict means fewer chances for Sylvanas to bolster her ranks. She is approached by Kil'jaeden, who makes an offer of making her more powerful, if she can dethrone the Lich King (Whom Kil'jaeden sees as being an obstacle rather than an asset, as Sylvanas could be). Seeking to increase the size of her army, she travels to Northrend with the Burning Legion at her side, to the frozen Bolvar Fordragon. While the Lich King sleeps, she steals his crown, becoming the Lich Queen. Bolvar Awakes, and the Scourge is conflicted. The Forsaken and some of the Scourge side with Sylvanas, while Bolvar and the rest of the Scourge aim to kill the 'False Queen' and stop her and the Burning Legion having control of the Scourge. Many of the Forsaken in the Horde oppose this, and a new leader is elected to help face Sylvanas (not sure who).