Yhwach was wrong to assume that Kyoka Suigetsu "wilted" or disappeared in any sense, because he was tricked by it. Also, as this chapter essentially proves that Aizen can use the Complete Hpynosis without the need for a sword, it would either mean that Aizen is either capable of using Bankai without one as well, or we'll never see it. All previous Bankai shown indicate that the sword in question undergoes a transformative process, whereas in Aizen's case, he has no blade to transform. So..I don't know. Your guess is as good as mine.He said he reached his limit as a Shinigami in the FKT arc, that's pretty clearly meaning that he has Bankai. He still has Kyouka Suigetsu, so there's no reason to assume he's lost his Bankai too.
Yhwach said "All Bankai's have been destroyed in the future" which could mean that he destroys Aizen's Bankai, but this is Aizen so he could just use Kyouka Suigetsu to make him think that happened.