The opening of the campaign is great and then the next encounters are going to be a great letdown for your players until they encounter the tribe. I would replace them for a combat with a minor demon or undead in the dark just after the fall.
Also the second and third NPC would be better combined together and given a typo about xp, I think they were originally so especially when you see the most interactions described are between the first NPC and the others. Other than this they are great
Finally the prestige points at the end of the adventure are a problem .
You are supposed to be in a race against time but your prestige points will depend on taking time to do side treks. Ok they are side treks good people would like doing but not when something more important has to be done before Armageddon .
As said in the title,this is nitpicking , the majority of the adventure is great and you can understand why the PCs are selected as heroes given the situation