Susan remained in 22nd century Earth to marry David Campbell in "Dalek Invasion of Earth" part 6, and she would be seen once again in "The Five Doctor's". Her later fate has not been revealed in the series proper. She obviously didnt survive the great time war as the Doctor is the last of the timelords
- Given the depiction of the Time War in "The End of Time", I'm not so sure we can completely rule out Susan's possible survival. In the first place, it's obvious the Time Lords are still "alive" in some sense; they just have no access to the universe because they're "time locked". So she could still be alive, but within that locked environment. Indeed the script certainly allows one to build a case for her being the mysterious "Woman" who talks to Wilf. But I personally think it's possible she's just alive on Earth with her family. The new Big Finish audio "An Earthly Child" posits this very notion. I suppose the possibility is mitigated by the notion that the post-Time War Doctors would have gone back to see her, if she were still on Earth. The fact that the Ninth and Tenth Doctors constantly bemoaned their fate as the "last" is evidence for some that she's not on Earth. But somehow I can't figure out how Susan would've ended up a combatant whom the Doctor needed to time lock.
In "The Empty Child"/the Doctor Dances, it's implied that Susan is dead.
Dr. Constantine: "Before this war, I was a father and a grandfather. Now I'm neither, but I'm still a doctor."
the Doctor: "I know the feeling."