You saved many of my closest allies today, <name>. I can only imagine what horrors you witnessed within Iso'rath, but you have the thanks of all of the Earthen Ring.
As with the previous quest, Earthmender Duarn will summon a healing bubble. Stay near him the entire fight.
You may find you have to abandon and reaccept the quest if your shaman companions don't spawn or if you cannot attack the brain. Make sure you aren't on your flying mount.
Immediately after killing the brain, a gryphon will spawn and automatically fly you out of Iso'rath. It is possible to die after this if your digestive acids bar is filled too high.