If you are working on your flame warden achievements, some news from Bornakk again:
"We are in the process of applying an in-game fix that will restart all of the quests associated with the Midsummer Fire Festival event and allow players to complete them once again. If you are in the process of completing an achievement such as Extinguishing Kalimdor, this fix will reset your progress and you will need start over. This fix will require realms to be restarted."
The point of this, I believe, was that many who had already done a lot of the quest components last year were not able to get enough burning blossoms to purchase the items needed for the achievements to get the title this year.
I have interpreted this to mean that any achievements earned will remain, while those that were merely in progress will be reset. Essentially, I believe, you will be able to get the same achievement twice.
Of course, for people such as myself, who had been slowly working through the achievements for Midsummer, I am now spending my morning dailies time scrambling to finish some of them off before they get reset during maintenance window.
Here's hoping that not too many others who spent the weekend working on their achievements will be in the same scenario as I am!