At the beginning of the game, the announcer says there are 58 participants. By the beginning of this episode, it appears that 30 or more people have already been killed. However, when Ariso accuses Aguni of being the witch, there are at least 40-50 people still alive in the room.
Its implausible Momoka would kill herself thereby initiating the witch hunt which leads to many deaths and the Beachs demise , when she wanted to stop being part of the games of death.
Likewise Aguni wouldn't lead the destruction after killing his friend because of the killing.