These are just random thoughts about Aizen dying.
1. Orihime may help kill Aizen through her power of rejecting reality, by either turning the Hogyoku's healing ability off or by reverting all the regeneration it has already done effectively killing Aizen.
2. Hitsugaya attacks him out of nowhere turning him to ice and shattering at the same time.
3. Yamamoto gets back up and goes Bankai.
4. Someone we have overlooked like Chizuru Honsho....