I don't know how great a promo this is - in two weeks Mrs. & I will be going DTW - TLV in BE & paid 215k miles each (we booked about 3 months ago). I just looked & they are now asking 350k miles each, so it makes no sense to cancel & rebook for this promo. But, it may work for a new booking a few months out (or has DL just raised the mileage for all trips to cover the promo costs?).