They are rebuilding it, but a lot of elements are carrying over into the new version, not to mention the community. The world's lore, the crafting, the items, the character designs - those will all be there. The only changes I really anticipate are a reworking of the UI (for the better) more in-game activities to do (for the better) and more places to explore (for the better).
"There's a time when a man needs to fight, and a time when he needs to accept that his destiny is lost... the ship has sailed and only a fool would continue. Truth is... I've always been a fool."
