I was on the Sovereign for the 3-night cruise a couple weeks ago. The thing with the formal night is that it is while in Nassau until midnight, so at least some of the passengers were ashore. I didn't attend the formal night dinner, instead opting for the casual buffet dinner. I did note a surprising number of tuxes and gowns being worn, but really, suits, sport coats and ties, and cocktail dresses are the most popular.
The cruise line will do what it needs to do when it comes to hurricanes. They never willingly head into a storm. It comes down to what happens with the storm path. If they have to change departure time, they will. If they have to leave early, they will. If the itinerary needs to be revised, they will do it. Over the past couple of weeks, all of the above have happened. Carnival and RCI changed itineraries. NCL had a ship leave Miami 2 hours early. The bottom line is they don't know what to do until the storm path and any damage it did at your planned stops becomes known. It can often be down to the wire. I had an itinerary changed while we waited to board once, because of a hurricane.
I suggest you keep an eye on this page
and also sign up at the RCI website for alerts about itinerary changes. You can sign up for e-mail and phone alerts here.