When the PCs open the Stone Roads and enter the Vault, how long does the way stay open behind them? Can they go back? Can they re-open it from this side using the shard, and if so, where do they need to be? Can they use plane shift to get back to Golarion? Can they make a tuning fork to use plane shift to get to the Vault, once they've been there?
How does the force at the Onyx Citadel 20 miles away send two groups in response to the PCs' arrival that seem to show up within a couple minutes? Neither group teleports.
What does the Stone Road opening up look like? It must be somewhat showy as the pech immediately notice and send a scout force.
This part didn't run well for me at all: too much key information is missing. I think most PC parties will be reluctant to go up two levels with no resupply (the treasure in the module being therefore almost entirely useless except for potions).