The docs for SC.Drag say that setting slideBack to YES in the hash of options passed on view creation will cause the ghost view to slide back to the original view's position if the drag & drop is not successful. Instead, the ghost view just disappears when this option is set to yes.
I've put together a simple sample app displaying this behaviour at https://github.com/OliverM/sc-DragAndDropSample
All the relevant code is in the main_page.js file for convenience. I'm not sure how to construct a test for this but if anyone has any advice on that I'd be happy to follow it.