Jake refrained from telling her that this could also be the work of their "allies. If it was Duke Gole, Haynt or Usadra (the only surviving seat of the Dark Races) who gave the order, then Rifalen might very well have chosen to cooperate to avoid unnecessary bloodshed.
All things considered, this theory was quite likely. After the Mutant higher-ups were killed or captured, the coalition that included the Mutants may have determined that their faction was hopeless and chose to cut their losses by raiding their treasure room before the enemy.
The supporting argument for this was the fact that the vast majority of the Mutant corpses lying around were mostly civilians. There were very few warriors and adventurers, except for those who had the misfortune to be there at the wrong time. The other possibility was that they knew what was going to happen and chose to stay.