Some time ago this happened to my friend on the front wheel whilst we were going pretty quick downhill. The tyre came off the rim and the tube popped out, wrapped round the forks and he went over the bars very very quickly indeed. Fortunately he got away with "only" a broken collar bone. The rim had failed along about 12" just like as in your picture. He bought some of the original Hope discs and had new rims every 12 months after that.