That's the reason why I believe so strongly that Goodra will return. (that sounded more dramatic than I intended it to be. "Goodra will return..." xD) Also note that they revealed Goodra's ability (Hydration). And there's a man in that swamp- the owner of that wooden hut. It all points to Goodra's return at the moment.
I think it is more of ditching Goodra to make space for future captures. The Noibat, for example. And there's every possibility he might catch a Phantump/Honedge/Bergmite in future. It is true that Alain made an appearance, and it was reinforced that a good bond between trainer and Pokemon is required for mega evolution. It does look like they have plans for a mega. Which of his Pokemon will mega evolve? Most probably Charizard. I think he will get his Mega sometime after Laverre..like you say, after the movie. There is most likely going to be a huge gap between Laverre and Anistar, or Anistar and Snowbelle. So we'll have Serena episodes, Team Flare, Malamar, a bit of Clemont and Bonnie, and maybe some AmourShipping too. And then a short mega arc. Probably.