Each player exiles all creature cards from his or her graveyard, then sacrifices all creatures he or she controls, then puts all cards he or she exiled this way onto the battlefield.
10/4/2004 The creatures which are sacrificed can’t be regenerated.
10/4/2004 Both players exile their creature cards at once. Then both players sacrifice all creatures they control at once. Then both players put all creatures they exiled onto the battlefield. If there are any choices involved for a given step, the current player makes their choices first, then the other player, and finally you do the action all at once.
9/20/2013 “All cards he or she exiled this way” refers only to the cards exiled in the first part of the effect. If a replacement effect (such as Leyline of the Void) exiles any of the sacrificed creatures instead of putting them into the graveyard, those cards aren’t returned to the battlefield.