I think Goodra's coming back.
Some interesting things have been brought up in today's episode.
1) The episode ends with Goodra chilling with them in the springs. We don't see them leave, and there's two weeks till the next episode. So maybe, as they leave, Ash asks Goodra to fight alongside him again for the league if it wants to, and so they head for the league.
2) Alain is collecting badges and now has them all. His motive is to fight Ash in the final round of the league. Ash is probably going to need a good team to do this. So old pokemon are fair game, but if he were to have Kalos only mons, Goodra could work quite well imo.
3) The descriptions for the next two episodes after the next, are interesting.
They state that while Alain fights Trevor, a trainer challenges Ash. Specifically it says this:
">The Kalos League finally begins! The participants in the league are all tough Trainers who have each gathered 8 badges, and among them are Shota, Tierno and Trevor, Trainers Ash and his friends have met before. Ash gets more and more excited, but then a Trainer suddenly challenges him to a battle."
This sounds like a non official match. So I wonder who could this be, and why?
Could tie into his capture if it is on the streets. Maybe Goodra has something to do with it, or could show up afterwards?
Although the next episode's description could be a hint for Goodra showing up:
">Fierce fights happen one after another in the Kalos League. Shota and Tierno go up against each other over a place in the semifinals. Shota has also made a personal analysis of Tierno, who specializes in a rhythm strategy that uses dancing to stay in sync with his Pokémon, and makes full use of it as he goes up against him. Both of them fight furiously with neither giving an inch, and the battle eventually comes down to the last Pokémon on each side. But then Ash and his friends spot something... but what?"
Perhaps while watching the match, Ash and co learn about how there is a goodra wandering the streets of Luminous. thus leading them to investigate. Then Goodra joins Ash for the league?
I don' know, I'm really thinking it's Goodra and he'll be invited to fight at some point in the league, but you never know what they might do.