A little late.. but here's what i believe would happen after Diantha's battle.
Poor Jessey, she was cheering for Gourgeist haha. I think we all feel the same as Jessey.

I have to say, I'm dissapointed we didn't see a full battle episode. I was hoping to see Tyrantrum, one of my favorite fossils ever.
But knowing it would lose like that, it would've made me angry.
After that tremendous defeat, We now have Leon waiting for his next rival at the finals.
Mega Gardevoir surprised me in that final battle, but sadly it wasn't enough.