We finished the adventure today. The players ended up teaming up with Gerplak to defeat the boss. Since I'm not sure what the next adventure is like, I made it unclear if she's dead or teleported out at the last minute. I'm ordering Colossus Wake from Exalted Funeral tonight!
We were curious about the stone lion. I'm assuming it was meant to protect the armory, but one of my players suggested that there could even be a magic item under the stalagmites that has been buried by stone over so long that detect magic can't see it. I could see a cool quest coming from that, where the players discover the stone lion defeated and the stalagmites destroyed and then have to go after the person who did it.
Thank you again for a fun adventure!