The guards easily fall for the ruse of the illusion, but the clerics, moving slower, in general, manage to spot him as he darts out the side room, and proceed to chase after the real Draiss, while the guards in front of him continue after the illusion. Unfortunately, unlike the guards, the clerics have ranged abilities, and attempt to pepper him with effects to slow, hinder, or stun him, rather than hurt him directly, since, clearly, that didn't work the first time.