Here is my hypothesis:
Revan and the Exile go into the Unknown regions, and make a huge dent in the Sith's plans, considering they delayed their attack by 300 years. Meanwhile, the Exile's crew members rebuild the Jedi Order, and Carth Onasi rebuilds the Republic Military on a stronger foundation.
Canderous Ordo rebuilds the Mandalorian, and they are once again a force, yet nowhere near as strong as they were under Mandalore the Ultimate, but at least they are no longer rogue bandits; they are united again. However, Revan's orders to Canderous are forgotten through the generations and the Mandalorians once again resume their badass selfishness.
Telos and Onderon are restored to their former glory, due to the actions of the exile.
Then, the Sith come and own the Republic, but at the last second let them keep Coruscant so that the cannonical events of the next 3500 years can take place . . . and yeah, that's what I think.
Let there be rock!
"I hope they realize that music is music, and that music is not a scene, not a style. Music is a beautiful ****ing thing to listen to. It is not a thing to ****ing preach to others about, it's not a ****ing cause. It is what it is—and that's a beautiful artform." - Synyster Gates
Check out my Fanfic:
Star Wars: Knights of the Old Republic II: Embers of Destruction