World of Warcraft developer, Zarhym, has posted a new blog on the community site giving players fair warning that some quests will no longer exist after the shattering that Azeroth will undergo during Deathwing's escape and the destructive forces unleashed on the world. If there are achievements or quest arcs that are nearly finished, it may be wise to log on and finish them as the approaching destruction is probably less than a week away, perhaps as early as 4.0.3a's arrival.

As you're all aware by now, the shattering of Azeroth will drastically and permanently alter the continents of Kalimdor and the Eastern Kingdoms. In the wake of Deathwing's devastation, adventurers will be summoned to embark on new quests from levels 1 to 60 in these transformed territories -- and with so much new content to be found on these original two continents, many original quests will no longer be available after the shattering occurs. These quests will automatically be removed from your quest log, while any quests you’ve accepted that still exist in Azeroth will remain in your log.

Read more here.