Looking over the vortex with his new [Mana Vision] skill, Cain can see that it is missing something, and that missing something is what is making it unstable. For now, he doesn't know exactly what it is though, so fixing the vortex is beyond him. The principles of Spell Crafting say that it can be modified though, which means he will eventually be able to fix it, or at least stabilize it and hopefully remove the people that are trapped inside.
If nothing else, maybe he can modify it a little and turn it into a dungeon.