I would agree with kenny. I would not be happy until I found the magnet, no matter where it was. I would scour the garage floor totally, clean everything up until the floor was completly bare and if not found, go back inside the motor and look again. If nothing else, to cover your own butt, since the shop charged you $200+ to look for the magnet and remove it, I would ask for something in writing that says it's not in there. That way, if it does surface inside later they would need to step up and help with the repair it would need.
Or, the magnet may just end up getting chewed up anyway from all those beefy steel gears.
Either way, I would not be able to sleep and worry everytime I stared the bike until I had that sucker in my hand.

A word to the wise is not necessary. It is the stupid ones who need the advice. Pat