@Akera93 I think it's a slim chance that the traitor is just playing part because it doesn't make sense as of now. Like why he/she chose to side with the demon king when the reward is relatively the same beside the fact he/she has to kill all 9 other to automatically advance to the 99th floor. But I do know that when you kill someone, he/she will die for good, since this isn't isekai nor a virtual game nor a dream (both are located in real world). The tower is connected to the outer world which is where that one guild master (one who can turn into cat), supervise the trading of food with the outer world since the one who entered the tower can't go out until they clear it.
As to the fact that if one of the 8 guys who recruited the MC has been a villain all along, it hasn't been explained yet. It could be that he/she's a real villain or just tempted because of the reward. The fact is that we can clearly trust the sword master (rank 1) since it was shown that he chose the goddess side and MC.