Everyone else down there was absorbed,excluding Minerva and keith.
Also,Happy was flying and he got sucked in too...was that magic absorbing everyone who was touching the floor or the walls of that beast,or did the beast targeted everyone down there?
If that is the case then Minerva and Keith probably escaped because they were demons..or they weren't touching the ground.
But this begs a following question.Why did those soldiers,supposedly demons did get sucked...and,more important,why Lucy wasn't as well?
Maybe Lucy survived because she wasn't touching the walls or the floor,since it ended before she hit the floor?Or did the cube not absorb her because it couldn't?it could be luck,still,it is weird.