@SpeedForceSpider: Oda made little Enel short story of him going to the moon and meeting Spaceys, they may tie into the plot at one point or another, so it is likely he will return but probably not soon.
It will probably be sooner than you think. Oda said this arc (Dressrosa) would involve the moon (already strongly hinting at Enel). He also said a new race would be introduced (faries probably) and we all know Enel was looking for Fairy Vearth. It adds up too well.
wow i didnt noticed that! actually that does make sense, moreover characters from that arc such as bellamy are returning which makes it even more likely.
There is seemingly no 'perfect' way to truly say goodbye. So I gathered a bunch of them!