I think they’ll resort to sensing aura’s and energy output to fight Aizen. There were seens were characters were doing just that. The other option is to use an attack that strikes in all directions with a massive radius (cause there is now way of hiding from that). Example: A Nuke, A Tsunami, A Tornado, etc. Characters capable of such attacks (depending on the author): Ichigo cause of his massive energies, and Byakuya who can send his cherry blossom peddles in every direction (alot of small hits can do as much damage as one big one. Plus, Aizen moving through an ocean of Byakuya’s peddles is like tossing paint on the invisible man).