User blog comment:Fallenbladr/Aizens Escape/@comment-3230060-20140818125104

You forget that Aizen may already be..."out". Anytime after Ywach leaves the prison I believe it's possible for him to have made his own escape. Consider, he could use his power enough to warp time observation for Ywach. Could he not also have used enough power to escape at that same point? There's also a very mild chance that Ywach is now Aizen is disguise.

As far as Tosen being alive, I kinda don't think so. Because if he were still alive, I'm betting he would have found a way into the prison in those first 17 months of prison time. But considering it's Bleach, I rule nothing out. I'm personally still holding out hope that Izuru is still around somewhere.

20k years may be nothing to Aizen, but it's probably not that much to Urahara either. If nothing else, Urahara would leave a plan in place with the science division...or the Captain Commander.