Where do Cats go in warriors if they are bad?

They go to the Dark Forest, or more appropriately named, the Place of No Stars. Cats who disobey the Warrior code (and not small things like disobeying Clan leader. Things like murder, betraying your Clan, etc.) will go there. It is described as a dark, cold forest with no prey, and you can scent several other cats, but it is VERY unlikely that you will meet them.