I'm pretty sure it used to be 60%, but then I think someone changed it to 40% before Necros are healed. It should probably be tweaked a bit. 60% seems much better, especially if they are not in combat.
Code:
// Give necromancers a chance to go lifetap something or cleric can spend too much mana on a necro
if(hpr >= 40) {
break;
}