User blog comment:Salubri/Aizen, Yamamoto and Wonderweiss/@comment-1429792-20100226233318

@ Aizen sorrow z:

Unohana thinks of Ichigo as having a chance against Aizen because he is powerful AND he has not been exposed to Aizen's hypnosis. Not just because of his power, but because he has the power to (possibly) hurt Aizen and the potential to actual hit the real him. The relevant chapters are 381 & 382.

Personally I'd take the "we'll both die in here" comment from Yamamoto with a grain of salt. I read it as fighting talk and showing he is truly prepared to sacrifice himself to kill Aizen. Not a guarantee that Yama will die in it. Just my personal thought on that one.