@faraday — There's several answers to that.
First off, even with really random test groups running, there's only been two obstacles that stopped a group dead in their tracks; I've tried to tune those two a bit more. Most obstacles have multiple ways to pass them with widely varied skillsets needed, so there's usually something someone can do. It hasn't always been easy, but generally groups have gotten through. But yes, this is dependent on good obstacle design.
Second, it's not intended that you run an entire good-sized Shardhaven at once; you may encounter an obstacle and have to backtrack to find another path, or even return to the city and research information on how to pass it, or find someone who can help, and come back to continue on another expedition. You might even have to flee when someone is too badly injured to continue!
Third, not all Shardhavens will be GM free. I'm intending to build a kit that will let players GM a Shardhaven for other players, like a D&D adventure module. They'll have the ability to spawn in monsters, any special loot that was approved when their PRP was approved, and so on. And they'll have a way to bypass obstacles for the group they're GMing for if the players come up with some really creative solution the obstacle didn't account for.