According to several matching reports from 2chan, Grimmjow's death is official. In his interview in the Jump Festa, when Masakazu Morita (Ichigo's VA) brought the arrancar arc into question and why it lasted for so long, Tite Kubo (Author of Bleach) revealed that Grimmjow is dead, and that he was actually supposed to die earlier in the series. It was the fans support that kept him alive for so long.
The japanese reports confirming Grimmjow's death:
583 :名無しさんの次レスにご期待下さい:2010/12/18(土) 21:12:53 ID:VoJ+JBMP0
自分の記憶の範囲で、ステージ補足。
My own’s memory
森田か折笠の、「今全体のどの辺ですか?」という質問に対し、
Morita/Oririn’s question “As of this whereabouts?”
「半分は超えている」と師匠。
“Past halfway.” Answers sensei.
それに対して「少なくても10年は続きますね」と言ったのは森田
Then in that case [It needs at least 10 more years to continue.” Said Morita.
破面編が予定より長くなったという事に対して、
As regards to matter that arrancar arc was longer than as planned.
「じゃあ、予想外に活躍したキャラはいますか?」と森田がきくと、
Then in that case, character’s unexpected activities were put in there? Morita asked.
「グリムジョー。もっと早く死ぬつもりだったんだけど、描いてたら
勿体無くなったんで、活躍させた」と師匠
I planned Grimmjow to die earlier, but when I drew it, I saw there was no emphasize at all, so I added activities to it.” Said sensei.