That sucks. Look down the hole with a flashlight. Can you see the end in there?
If not, have someone push the buttons momentarily to see if you can bring it into a position that you can see it.
Now you just need real fine pliers. The kind that hobbiests use to work on ships in a bottle maybe?
Alternatively, from the shape of the unit, it appears that it would just wrap around the core. That and it may have a chance in hell of rethreading on the way up. I haven't tried this, but you don't have much to loose at this point. Send it up for about a second or so. If nothing comes out, send it down for 3 seconds. Repeat. From the shape of the motor unit assembly I'd say you've got about a 1:50 or so chance of it coming back up the hole. I've never had to try this though.
My experience with my antenna... It had broken right at the point where the metal threaded bit sits on the end of the nylon wire. If this is the case for you, your motor still works and you still have enough nylon wire to make it work. You just need to do some fishing.
Good luck on it!