I'd say that there is always the chance that the cruise price will go down. But, if bookings are not up to expectations then the likelihood of that happening before final payment is probably pretty slim. I think most reductions will happen after final payment and after you are locked in to a price. So, if you need to be sure up front, I'd advice to book with a company that is flexible up until final payment and then just let it go knowing that you may have paid a little bit more for the certainty of the cruise. The other option to is book the airfare with miles now and hope the cruise comes up at a discount while being willing to cancel it all if things don't work out. Definitely risks to that approach as well.