The more I think about it, the more I realize that this spell will not be used much.....
The problem is that as soon as the zombie leaves the 30' sphere of control, it becomes uncontrolled. Not too bad of a restriction. But the other time that the zombie becomes uncontrolled is when the binding ends. Since binding spells end when the caster is vanquished, this presents a tactical problem. Odds are that the closest target to the now uncontrolled zombie is the vanquished caster.
Yea, letting loose a hard to defeat Elite Zombie mid combat is kinda tough. Especially when the one party member most equiped to defeat the zombie is down. So I guess I will shelve this spell for NPC use.