http://www.youtube.com/watch?v=L4mJfsIPPfw&list=FLERl6LWxTiLFhHuJX7ddqlw&index=17&feature=plpp_video
watch the fw190 was my dads nobody really knows what happened. He had tailwheel problems he thinks the plate he had the cables hooked to came loose and disconnected his batteries
I had that happen with one of my planes about 20 years ago. I had an aileron that started to flutter in a dive, and as soon as I touched elevator to pull out it just disintegrated the wing.
That may not be what happened in your dad's case, but it'd definitely possible.
I also had a friend who's wing wasn't strengthened enough where the left and right wings joined, so he ended up folding his wings in a dive and they came off.
The difference between our cases was that with flutter, my wing came apart. In his case, his wings remained intact, they just came apart at the joint and came off the model. His fuselage lawn-darted, but his wings fluttered down and were still in good shape when they hit the ground, lol.
I doubt the battery connection had anything to do with it. If it had, the plane would have just gone in but would have been intact until impact.
It's definitely a bummer though. Lots of money, time, and effort, to lose like that.