The ilidian its not working anymore. on the second phase after you kill those 2 green elementals, he jumps in the air and that's it. makes him not "killable"?! ( i guess that's it )
I heard that if you are a rogue and you vanish you can redo it.
but if you're not, and you use the hearthstone , wich is the only way to get out of there. you will not be able to start the encounter again.