World of Warcraft will not bring about the end of the Horde. It will, however, mark a crucial turning point in the conflict between the Alliance and the Horde when both sides storm the walls of Orgrimmar to take down Warchief Garrosh Hellscream. It remains to be seen just what will happen after tomorrow's patch, but as the preview video past the break shows, things won't be the same after the walls come down.
Not that the patch is just about laying siege to the Orcish home city. It also introduces flexible raiding modes to allow groups of any size to tackle raid content as well as the Proving Grounds, which are solo instances that test your tanking, healing, or DPS skills. There are also currency conversions and new items to be obtained, helpfully explained in a small FAQ on our sister site. Do what you need to do today, and get ready to storm the walls tomorrow.