Ahoy there, Ashlee, and welcome to planDisney! It sounds like you’re already on your way to an incredible adventure aboard the Disney Wish, so I’m hoping I didn’t miss the window to respond before you embark.
The quick answer is yes, when the itinerary changes due to weather, the daily activities typically shift along with the new schedule. This means that events originally planned for your Day at Sea will now take place on your updated 
Castaway Cay day (and vice versa). Of course, schedules are always subject to change, so the best way to stay up-to-date in real time is by checking your 
Disney Cruise Line Navigator app daily.
Disney does an amazing job at making these transitions smooth, but if you ever have any questions, don’t hesitate to head over to Guest Services on Deck 3. Even during inclement weather, the Disney Cruise Line crew shines brightly, making sure there are plenty of onboard activities to keep everyone engaged. A rainy day at sea is also the perfect time to fill up a popcorn bucket and catch a First-Run movie in one of the theaters. 
Here’s hoping Olaf’s Picnic and your entire sailing go off 'snow' beautifully! If you think of any other ways my 
planDisney pals and I can help, you know where to find us!
SEA ya real soon, 
Sami