Regina was dragged into the Dark Dimension due to the shackles of the maroon chain that Aerith had taken out.
After the valkyrie was fully trapped in the place, the dimensional crack shrank and disappeared, leaving Aaron alone in the floor boss room.
[CONGRATULATIONS!]
[You have successfully completed the Dark Pillar's 80th boss challenge]
[The next floor of Dark Pillar Tower has been unlocked]
[Floor Access Privilege: 81st]
[Want to go to the next floor?]
[Yes] [No]
Aaron was somewhat surprised when the success panel of challenging the floor boss appeared in front of him, even though he only pulled Regina into the Dark Dimension.
It is possible that the power that Aaron appeared as one of the powers that wiped out the existence of the floor boss, considering that the real world and the Dark Dimension have no connection with each other.