Im not sure about that actually. The hougyoku left him, only leaving him immortal. And it is said that when a zanpakutou is destroyed yet the user remains alive, the zanpakutou will reform. I have even wondered if he was able to use it before he was imprisoned. If he recovered his zanpakutou, he could have tricked everyone into believing that he was imprisoned while the real Aizen is at large again. Basically he could have repeated the same plot again and nobody would know better. I even have a strong belief that he is the one who rescued Urahara. Just look at good pictures of Kyouka Suigetsu and the sword at Urahara's neck. They have the same unique color theme! Of course I might be very wrong, but one way or another I do believe we will see Aizen again and probably sooner than we think.