JKR tied up most of the loose ends quite well. Mugglenet.com had put together a list that was almost entirely covered.
A few that remain:
Who will lead the Order now that Dumbledore is dead?
What lies beyond the veil in the Department of Mysteries?
Where did Fawkes go at the end of Half-Blood Prince?
How exactly did the Potters and the Longbottoms “thrice defy Voldemort”?
What’s behind the locked door in the Department of Mysteries?
JKR said that someone will manage magic very late in life in Book 7: who will it be?
And a few about Godric’s Hollow:
[INDENT]How did Volemort get his wand back?
How did Dumbledore know what happened there?
How was Harry found with Wormtail as secret keeper?[/INDENT]Anyone else have loose ends that I missed?
There will be/are a bunch of loose ends now about various people (I believe we only have glimpses from the epilogue about, Harry, Ginny, Ron, Hermione, Draco, Nevill, Hagrid and Mr. Weasley,) and there is very little about them.
I imagine that Rowling will be continued to be asked (hounded?) by curious fans. She may choose to put out a bit more ‘canon’ material that covers this. Personally I hope not—she created the universe and should get the chance to determine exactly where the coverage stops. But she seems so nice to fans that I doubt that she will ever them to ‘shove off, I’m DONE.’ Someday, maybe she will authorize a ‘behind the scenes’ look at the HP universe (sort of like Tolkien’s History of Middle Earth and letters).