I guess Believix really was only to be used to convince people of Earth to believe in magic, because as they fly back to Magix, all the girls are back in their Enchantix forms! But, wait, what about Roxy? She doesn't have Enchantix!
Roxy was excluded from this scene, although she was seen flying with them (all in their Believix) seconds before. So, is she not coming back to Magix and joining Alfea? What a cliffhanger to leave us with on the last episode!