https://learn.microsoft.com/en-us/dotnet/api/system.windows.dragdrop.previewdragleave?view=netframework-4.8.1
DragDrop.PreviewDragLeave Attached Event (System.Windows) | Microsoft Learn
Occurs when an object is dragged out of the bounds of an element that is acting as a drop target without being dropped.
event systemdragdropattachedwindowsmicrosoft