At the very end, the cake is shown to have one slice removed. However both Loona and Mrs. Mayberry each have have a slice of the same cake.
In the final scene, the main cast surrounds a cake celebrating Moxxie's assassination. In this scene, each character besides Moxxie is animated laughing, but the only laughter audio playing is for Millie and Mrs. Mayberry. Blitzo and Loona are not heard laughing with them.