We have had cruises re-routed twice. Once was due to weather and they basically just reversed the whole cruise. We didn't end up having a day of rain on the entire cruise and was kind of nice that they were able to make the most out of the bad weather. The only thing that we weren't able to do was to go to Grand Cayman since they tender you into shore so they gave us an extra stop in Mexico.
The second itinerary change we had was due to another ship that was on fire. We were the closest vessel to it so according to maritime law (or whatever they told us), we had to stay near it in case the passengers needed to come on board. We ended up missing our stop to Grand Cayman since we were just parked out at sea for a day. I was a little irritated at first at we missed our port, but then after I saw the 20/20 show on what the people on board the other ship experienced, I was very grateful it wasn't us.
So basically - it worked out just fine in both cases, just be sure to be prepared to go with the flow. They have dealt with it a lot and will make it work.
Have a fun time! We aren't sailing for another 2 months.