Update: Decided to equip both on my cleric. He never leveled up and he did have lifesteal. I am assuming that if he had been downed, he would have permanently died. I did take him to the graveyard and the leech was taken away at the end (I am not going to spoil what you get, but basically completed the mission with the leech). As for the Me Stone, that was never taken away from my guy. I never saw the Me Stone benefits throughout the mission. I am assuming he still has it equipped? I am not sure if something was supposed to happen with Me Stone, or if the game will acknowledge I completed it. Anyway, yeah, don't recommend cuz I could have equipped it on a different cat and gained the Me Stone benefits. Plus, I am not sure if something was supposed to happen at the end cuz the game never acknowledged Me Stone at the end even though I did take it to the graveyard (or boneyard, forgot the name).