User blog comment:Xilinoc/Ch. 563 - SUPERSTAR NEVER DIE/@comment-1706259-20131227165911/@comment-5218928-20131231004034

Some say to take the explosion of the 1st Division Headquarter as a sign that Aizen was killed off-stage. Ywach would've said that Aizen "had all of eternity to consider" after turning down his offer to join the Quincy/Wandenreich as a metaphor for killing him (he's a Special War Asset, after all. Ywach wouldn't want him to be a loose cannon; same with Ichigo, but he failed to capture him. Twice, too.).

Kubo being Kubo however, no one knows for sure.