User blog comment:Xilinoc/Ch. 670 - The Perfect Crimson/@comment-11398218-20160414113334/@comment-5398287-20160414134653

Well, in shonen whether or not a character gets brought back by fan demand can boil down to how hard they were killed. For example, in JoJo's Bizarre Adventure (SPOILERS), the character Muhammed Abdul was shot in the head relatively early on in part 3 and treated as dead; near the end of the first half, due to fan demand, he came back and claimed he'd leaned back to dodge the bullet and stuff. Then much later on he was erased from existence. Didn't come back from that.

Now, Byakuya got shredded by his Bankai, but was still kinda in one piece, so even though Haschwalth said he was dead and he said he was dying and by all rights he should have died, it was I guess believable enough that he could survive somehow, integrity of the story aside. Compare that to Ulquiorra, who literally disintegrated into dust - even the editors must've realized that it'd take a particularly large butt tug to bring him back after that.