Why put Sprite in a baking recipe?
The soda does a few things:


adds moisture to steam the dumplings.
cooks down into a syrup to make a sauce.


You can typically change out the soda, but you don't want to use a diet soda, as it won't thicken the same and some artificial sweeteners will break down when heated.  You don't just want to replace it with sugar water, as the acid in the soda will help to keep it from seeming overly sweet.