Strictly speaking the Citadel DLC is supposed to be before the game's ending, hence no, nothing is fixed.
When I first finished the game I felt sure that some of the future DLC would address the obvious Citadel attack problems - like WTF happened to everyone?! Through a combination of DLC schedule leaks and data mining, it became pretty clear early on that one of the later DLCs was going to be called 'Citadel'.
There's a certain argument that we play as Shepard, we follow Shepard's crew and ship, and neither were present at the Citadel when it was attacked. Some responses to that line of argument - 1) In ME1 we cut to Saren aboard Sovereign, so we're not always restricted to Shepard's POV. 2) In ME2 we play as Joker FFS! 3) Why not utilize Al-Jalani? Have her broadcasting a reporter's view of the attack as it's happening?
As it is, it's just a glaring omission. An omission that wasn't really helped by Gamble's Twitter canon - where he said that everyone of importance survived. Well if that's the case, would it really have killed you to insert a solitary slide as part of the end-of-game slideshow? Like the one above?
So many schoolboy errors....