After killing Bonegrinder, when you return to Arokh is when you do this. Headhuntress, I think, jumped off the far left cliff face into the water where you killed Mezzidrel. I tried and tried, but couldn't make that jump...so... I flew Arokh over to the right side of the little lake area. There's a little mesa after a green patch of walkway, and I landed Arokh there. If the game forces the cutscene to save on you, just hit the 'start' button to return to the game. I dismounted and walked the rest of the way (there are a couple of small jumps, but nothing that'll take any health) onto the bridge where Mezzidrel's heads lay, and jumped into the water. I swam to the alcove with the cave off to the left, made landfall, and called Arokh. He answered and began flying towards me. Then I swam over to the main island face where the docks are and he landed. If you stay out of the area that triggers the cutscene, you can go anyplace in the Isles that you want. It's perfect.