Cultivators being what they are, often very willing to sacrifice others for their own greed, the alchemist guild should possess some safety mechanisms. Like the old branch master should pay a visit to check on Yang Kai and any newly appointed guest alchemist at the various sects in the surrounding areas. In conjunction with that, it could be expected the guest alchemist would notify the guild if they planned to leave a sect and move elsewhere. So, if the sect just claimed the alchemist left and the guild has no knowledge of it, it could be suspected the sect is up to no good.