The entire deposit is non refundable. You can change sailing dates or change ships for a $50 per person fee and the deposit is applied to your new dates but no refund.
My choice would be to book with Carnival and watch the price myself. Agents are booking many people so they don't always have you as a priority. The price drop will not happen unless you submit the online form.
8 Norwegian: Sky, Jewel, Dawn, Epic, Pearl, Breakaway, Getaway, Escape
10 Windjammer: S/V Legacy X3, S/V Polynesia, S/V Caledonia, S/V Diamant, S/V Sagitta X2 S/V Mandalay, S/V Vela