Though it's improbable that's the canon ending. I don't think that Croix would be the type to "wait-and-see what happens".
Especially compared to Jakuri's ending, where he goes back with her to Sol Ciel.
As far as I care, that's canon enough. For one thing, our 3rd reyvateil deserves that happiness. Luca and Cloche can have their lil sister love thing going on for all I care. :p