I've had this happen to me a couple of times on a steel frame. I think both occasions necessitated a trip to a friendly framebuilder for some brazing and a respray, and both occasions certainly wrecked the derailleur (On the first, the pieces had gone "sproing" all over the road). I think my back wheel survived both times, but I'm not sure about that.

These days, I'm very careful about the bottom stop on the rear derailleur, and anything that might have disturbed it merits a careful check before I ride the bike.