Sorry, but you can't have invincible characters in a game like this. If I can use any character as a projectile to deal damage, and they can take damage, they need to be able to be killed.
I think this might be a bug caused by throwing, because I've had, on the rare occasion, the harpies attack and kill Mirkon. Is it possible they gave him protection from the player but not from the harpies? So the game bugs out when the player uses him as a weapon.
