Didn't seem to work on Ulquiorra but then again he was dusted. Also Aizen lost his Zanpakuto when he changed forms and the hogyoku decided he no longer needed it, not when he was hit by mugetsu; that doesn't mean its gone for good however. Ichigo got his Zanpakuto back even after he lost his powers and several other characters who 'lost' their zanpakuto had them recovered(even people in the filler arc whose swords were destroyed instead of resealed, filler wasn't canon but still)
Acutally he still had his Zanpakuto, he even told Ichigo how the final form of their Zanpakuto are the same because they were fused to their right arm. Even at Aizen's final transformation he still had his Zanpakuto, but it was after he was hit with Mugetsu when his Zanpakuto was crumbling away, thinking that the Hogyoku claims he no longer needed it. As far as Zapakutos being recovered, remember Captin Kurotsuchi can repair damaged Zapakutos, he even broken his Zapakuto a couple times because his Zapakuto turned on him. Can they repair Aizen's Zapakuto, they can, but I think it gone for good since it fused with his hand/arm it complete broke down and vanished. For Ichigo getting his Zanpauto back, he never really lost his Zanpakuto, he lost his spiritual powers and the if you remember back at the 1st arch, Rukia mentioned that the size of a Zanpato is determined by the spiritual pressure. No spiritual press = no Zanpakuto, which is why when he got his powers back he got back Zangetzu.
