If a deck breaks on a single stolen creature, it is really a crappy weak deck.
So, i guess, conversion is ok with the miracle cost (12/10 + drain all).
The only thing i hate is the converted skill usage.
I have 3 optional suggestions:
1. poison the stolen creature, it will die and be gone + convert skill
2. strip the skill, but keep the creature
3. poison, keep the skill as original quanta, but give the creature back to the owner's hand after it died from poison
Maybe 3 is a bit too complicated.