The Warden can sacrifice him- or herself.
Alistair can become King without any Queen.
Leliana, if romanced, will fall apart from grief if The Warden sacrifices him- or herself in the final battle. She will claim that the Maker has spoken to her again and told her she will finally be reunited with her passed away love.
Morrigan was last seen traveling the Frostback Mountains, possibly with child.
Oghren can also become the first dwarven general of the king's forces, if Alistair is declared king.
Shale might go to the Tevinter Imperium with Wynne to seek a way to regain her mortality.
Sten can return to his homeland.
Wynne might follow Shale on her quest to regain her mortality.
If the player dies killing the archdemon, Zevran returns to Antiva and become leader of the Crows.
Arl Eamon will stay on as an advisor to Alistair if Alistair is made king. Eamon eventually abdicates his arling of Redcliffe in favor of Bann Teagan, to the approval of the townspeople. Should the Warden also give Kaitlyn enough compensation for her grandfather's sword, she will eventually meet Bann Teagan and the two will marry.
Alistair might grant the City Elves a place in the council.
Anora, if Alistair is made king and she does not willingly abdicate the throne to him, is imprisoned in the tower to avoid a rebellion (at Alistair's request as he does not want her executed—a measure of mercy an appreciative Anora admits she would not have shown were the roles reversed).
If The Warden allows Brother Genitivi to mount an expedition to the Urn, and kills the High Dragon, the temple becomes a mecca for pilgrims.
If The Warden is not a mage, who completes the Broken Circle quest and sides with the mages: "Following months of effort, the tower of the Circle of Magi was finally cleansed of the last spirits to slip through the Veil. No further abominations were created, and First Enchanter Irving was pleased to declare the Circle safe. All that could be saved had been."
If Harrowmont becomes king, he further isolates Orzammar from the surface world. Harrowmont will eventually die - suggested he could not handle it anymore, or was poisoned.
Siding with Harrowmont and recovering the Anvil will also lead to a decline. Harrowmont will discourage trade with the surface leading to further isolation, in addition after Harrowmont refuses Branka more volunteers for the Anvil she will begin raiding the surface world for the needed ingredients. Eventually the surface world will retaliate and some of Orzammar's tunnels will collapses in a battle - cutting off all access to the surface.
If you helped Brother Burkel near the Tapster's and convinced the Shaper to grant him the right to preach his sermon's to others, he will end up converting quite a few souls to the Chantry. The majority of the rigid dwarven populace will not react well to this, and Burkel is killed while resisting arrest. With his death, the Chantry itself will then consider leading an Exalted March on the dwarves to avenge this perceived slight upon their religion. It is unknown if they ever do go through with this however, as it is only suggested during the ending credits.
If you help Dagna join the Circle of Magi, she will later author a comprehensive theory of how lyrium vapors relate to the supply of magic. It gains a great deal of attention and inspires mages from other parts of Thedas to establish a new circle in Orzammar itself, one that has ready access to dwarven lyrium... and lies outside the chantry's power completely. The willingness of Orzammar to harbor Apostates sparks outrage that begins whispers that the Divine is contemplating a new Exalted march.
The Werewolves might have been cured by The Warden and returned to Human civilization.
If The Warden saves the Dalish they will become more respected due to their part in the final battle and their connection with humans will steadily improve, but tensions will eventually rise again. Lanaya, the new Keeper, will be instrumental in maintaining the peace between the humans and the Dalish.