How to revert an item's state to "Normal"?

Hi, I'm wondering if it's possible to create a trigger that will revert an item's state to "Normal" if there is nothing on a particular drag target when the "Submit" button is clicked?  I have created different states that are triggered when different items are dragged onto each drop target (i.e.: five drop targets have five items (1, 2, 3, 4 and 5) that are supposed to be dragged on top of them - the states of each target change to correspond with the most recent item that was dropped on it but there can only be one on each target at a time).  Because this is a freeform Drag & Drop and there are no "right" answers, it doesn't matter which one is on which target when the user clicks "Submit" but if the user happens to drag an item OFF of a target and there is nothing on it when the user clicks "Submit", the state will still be from the last one that had been on there and the result will not be correct.  I also want to be able to create a warning that will keep the user from advancing if all of the targets are not covered when clicking "Submit", which I can't do if I can't identify whether or not there are any uncovered targets at the time.

I need a trigger such as:

(Change state of "Target1" to "Normal" if ....Object "Item1" dragged OFF... "Target1")

or

(Change state of "Target1" to "Normal" if ...."Target1" is EMPTY when user clicks "Submit")

or something of the like.

I don't think those conditions currently exist, though, so I'm wondering if anyone knows of another way to reset those states to Normal if an item is dragged off of them again after being dragged on?  Any brilliant ideas are welcome!