It's your status on the day of departure that matters, not when booked. That said, sometimes status levels can be "sticky" in the reservation so it's possible that the system would still show your old status and you might get upgraded based on that. But if the "system" refreshes your reservation or anything, then it will likely be reset to your new, lower status and that is what your upgrade priority would be based on.

If you old status holds in the reservation consider it a gift, but you should plan for/expect the lower status to be reflected and shouldn't be miffed if that is how it goes down.

Regards