The players can't drive the story. The best the players can do is to roll to find information, and hope they fail enough rolls to trigger the ending. The information can't lead them to the enemy, and the situation can't be resolved until they confront the enemy, so a spate of good rolls results in the players learning every rumor but not triggering the final encounters.
The module itself is poorly edited, with several typos.
While skill-based modules are sorely lacking -- there are plenty of modules where you lose unless you can defeat the BBEG in combat, there aren't enough modules where you lose unless you can make a DC X skill check in skill Y -- this is a poor attempt at it.
I recommend against playing this. You could do everything right, but fail one save and have your character gets a permanent penalty. The module might as well had the GM say "Welcome to Bonekeep, everyone roll a d20, and if you roll a 5 or less you get a permanent -2 to saves vs. fire spells that nothing can remove."
I wouldn't have minded if my character died, even if by a critical on a sneak attack, but this depended entirely on luck and you can't remove the condition. It reminds me of the arbitrary and random days of being a kid playing D&D, and I expected better from Paizo. I'd be as disappointed if characters randomly got a permanent bonus on saves.
There's a big difference between "tough" and "depends on luck".