I made my final payment to Norwegian for my cruise Tokyo to Seoul.
I do not know if all cruise lines operate the same but with Norwegian you have to pay off the entire cruise four months in advance or the cruise is cancelled.
My memory is that it used to be three months in advance.
Now, here is what I am going to predict will happen. The price is going to drop and some times by quite a bit. If it drops before final payment, then you will get money reimbursed. But if it drops after final payment, you may be given some perk. You might get a Future Cruise Credit or some On Board Money in your account or you might get upgraded.
I say may and might because it is not guaranteed. And then you do not know what you will be offered. Take it or leave it.