You don't have to leave when you get the immortality buff. Just go down on arena and stay near the wall. At the end take a SS that you didn't heal or kill anyone (so you didn't abuse it).
PPl from the other site should be aware thou, that even if those whit the buff don't kill/heal, they still can take chests, use fear/blinding etc., so be prepared and make screens of such behavior - it's abusing the bug, and post it so they can be punished.
btw. both sites are abusing the bug.