After you answer the statue's questions correctly, you get experience and a level of Restoration. I don't think the cult would follow you around if you had gotten the answers wrong, but the correct answers are;
1. Experience
2. Truth and Untruth
3. Good, Neutrality and Evil
The portal appears when you kill the 4 frogs. If you don't get the portal doing so before talking to the 3 guys out front (I would have thought Blake's hint would have been enough...), you can still get to the treasure room (though there is only a frog statuette and some gold there);
FIX for the Missing Catacombs Portalor
Teleporting Anywhere, via hex editor