It's rare that NCL will cancel. A re-routing is far more likely, as they are doing with Norwegian Spirit this week (sending her to Bermuda instead of Bahamas).
We are keeping track of NCL itinerary changes in this thread
We were in a similar situation on Norwegian Majesty in 2005. Tropical Storm Irene was in our path to Bermuda (she wavered between a T.S. and Category 1 hurricane). A few days prior to the cruise, I started looking at Canada/New England ports, thinking that this is where we might be re-routed. Turns out that we ended up going to Bermuda after all, and the ship rode through the waves like a champ. That first day out was a little rocky, but weather was superb afterward.
BTW, you are on Norwegian Majesty, correct?