Everything Delta does is based on your status at the time of the situation. If you are gold and cancel an award ticket after becoming Platinum you pay no redeposit fee. The same should work with seats. If you are Platinum and turn gold, you should loose your free upgrade. If you no longer hold status you should not get the free upgrade. Seems only fare. Granted, you will likely keep the seat if nothing happens along the line (equipment change, schedule change etc) that causes you to be displaced.