If you are about to wipe, and you dont wanna die, go stand on the spot shown on the screens.
Worked for me 3 time in a row. Gruul cant get to you, or even hit you, so you'll leave combat, and will be able to walk back to the gate once he is back to his spot.
Note: Get an pot ready, he might be still in combat chasing other raid members, and then trow cave in on you (cave in can reach you), so if you arent an healer type, you might need to take an pot on this part.
Note: HUG THE WALL WHEN YOU WALK BACK TO THE GATE.
Go stand between the left wooden stick and the wall (just above the cross, abit to the right):
Stand here:
Tip: Check the minimap.