Seven days ago, the moment those four got close to that city, Darian could clearly sense everything inside it through the karma of the people within.
He located, deep underground in one part of the city, the forge where all the Heavenly Elemental Spirits were imprisoned. Once he knew where they were, he came up with that whole plan to sneak into the ruins, already sure he'd be able to escape afterward.
He even made a point of flashing the talisman to the beasts, making sure they believed he had teleported far away. But in truth, he had only shifted down into the underground. Of course, the beasts would figure that out soon enough, but he only needed a few minutes.
Since that race was basically made of tiny runes, Darian could gather them together, linking them with the power of the ring, just like he'd done with the three youths. With that, Tir could dig a tunnel out, and Awel could guarantee a fast escape.