Right before MC decide to sign, the floor where they are suddenly falls apart (ex-machina moment), sending them all several floors below. Simon and cia hit every thing on the way down, breaking most of their bones, but since the wizard girl end up betraying Simon, she make sure that the MC and the girls have a safe landing, but this floor is full of Orcs. Well, she helps the MC fight the orcs, but its too much for them, even after the other girls wake up. They decide to flee with an item as soon the boss of that floor shows up.
So, Simon, being a son of b*itch until the end, decides to make use of the slave collar, trying to escape as well, but the wizard girl stops him. She, Simon and the other two f*ckers are left behind to be eaten/r*ped by the orcs while MC and his girls escape with the teleport item, this being the end of chapter 64 (I didn't find the chapter 65 yet)
In the LN things were a little different after the fall. The way the wizard girl helped them was more "discreet", so the MC didn't notice and at the moment he got the teleport item, he left Simon, the wizard girl and the other two behind in cold blood. Only after they got out of the dungeon, the MC notice that she was helping them and decides to go back to the dungeon to rescue her. As soon they were leaving, the fat noble shows up, thinking that his plan was a success and now he have a new slave, but the slave collar was deactived long before his arrival. Well, he notices it too late and end up beaten by the girls of the MC party, the slave collar is put on him and right before his arrest by the royal guards (if I got this right), the MC put a curse on him that make his blood literaly boils everytime he gets too close to the girls.
When MC get back to the dungeon, he finds out that Simon and the wizard girl survived because of their special itens. Simon's armor gives him a regeneration ability, while the wizard girl have a item that hides her presence. The other two got eaten by the orcs (Maybe I got it wrong, but it seems that the other girl was actually r*ped by the orcs, according by some people on the comments of the LN). Anyway, the MC is finally done with Simon's BS and after their fight, the MC puts a curse on Simon. It's some kind of "degenerative poison" curse, which cause Simon's body to partially melt from inside out, causing insufferable pain until the death, BUT since his armor continues to regenerate his wounds, he's put on an eternal loop of pain. While agonizing in pain, he start to beg (and talk sh*t between the lines) to be forgiven, but since the MC is done with him, he leaves Simon in his eternal suffering and finally rescue the wizard girl.
At this point, the entire kingdom already knows the truth about Simon's team and the fat noble's dirty business and since the wizard girl was the only survival from the group, she gets all the punishing for Simon's actions. She regrets her actions, the MC forgives her and even offer her a place in his team...
Well, that's it. The LN still go on after this, but I decided to wait for the manga here.