If they attack at the wrong moment they could get caught in a hero quest, perhaps representing Sheng Seleris and his hordes invading the moon. If they succeed they carry away magic stolen from the moon - perhaps magical immunity to some Lunar magic. If they fail, or rather if the Lunar loyalists realise what is happening and correctly enact the return of the Red Emperor and the defeat of Sheng, the raiders not only end up captured and in very big trouble, but they might end up magically damaged in some way, perhaps lose the ability to communicate with their god for a time (isolation in "Lunar hell").
But the rival khan winning implies the rival khan placing religious faith and the good of the tribe above temporal power - enacting the ritual defeat of Sheng would require the current leader stepping aside, and appointing a new khan during the heroquest (the returned "red emperor"), who could then magically and temporally defeat the intruders and win magical boons for their tribe.