I'd second the suggestions that people have made for getting a backup room for that night.
But I would constantly check, or as others point out call the hotel and see if they can help you by giving you first dibs on anything that opens for that night (I've never tried this). I have had good luck with this property, last year I started building out 2 rooms for 6 consecutive nights with FFNs and although it took a lot of work I finally got it all cleared so that we had a completely free stay. Toward the end we had a couple of expensive paid reservations tucked in, but given the overall value of the entire stay we were prepared to pay. At the very last minute, those 2 nights opened and we used FFNs and cancelled the paid reservations.