they spent all those chapters trying to kill him just to let him live. what the hell are they going to do when he gets out in 20,000years?

Damn it old man!

maybe he's getting Alzheimer's and immediately forgot EVERYONE AIZEN STEPPED ON, FATALLY WOUNDED, TOOK ADVANTAGE OF and oh, I dunno...maybe the whole "I WILL RULE THE WORLD (soul society & human world) THING"....
Or maybe all that crap Aizen did bounced right off of Yamamoto's shiny bald head?

Alright, so I think this is an odd question for multiple reasons, the main one being...um...
Isn't Aizen immortal? Am I the only one seeing this? I mean, sure, there's a chance he's not, and in my opinion the best punishment would have been "know what? Let's test whether he's actually immortal!" Immortality means even Yamamoto can't kill him, period.
But there are others. We've all known that Yamamoto cows down to Central 46, and will continue to do so. What's so surprising about yielding Aizen's punishment to them?
I'm sure we'd all have liked a better punishment for Aizen, but you guys are acting as though this is somehow Yamamoto's fault. It's the fault of Central 46, the fault of the system that he's locked into. I blame them for this, not him.

I somehow respect Aizen a little and to just kill him off and be done with it is just too easy and lame.
since shinigami have long lifespans or they're immortal he should stay encased in a prison and if he gets out in a few centuries, well, fun will start over again xD

"off with his head!!!"- queen of hearts
what she said! Lets go with that ^^