Hello Jennifer!
Your magical vacation will be here before you know it! After a fairly exhaustive search including contacting a friendly Walt Disney World Resort Cast Member I can't find anything that indicates that
Pizza Planet will be closed during your upcoming visit. However, things can change quickly at the Parks, so I think you are wise to have some alternatives ready. While I don't know if any other location where the Cappuccino Cupcake is available, I do know that there are many amazing treats throughout Disney's Hollywood Studios. My favorite is the Carrot Cake Cookie that is available at both the Writer's Stop and Sweet Spells. Both of these locations also have a variety of great treats that should help with almost any craving.
We love Pizza Planet, but when we need to choose an alternative we tend to head over to the end of Sunset Boulevard where there are an array of choices including Fairfax Fare and Catalina Eddie's amongst others. This area is great because the closeness of the quick service locations makes it possible to please nearly everyone.
I hope this helps with your planning. If you have other questions, come on back to the Disney Parks Moms Panel- we love to help!
See ya real soon,
Anne