Well there is the league that they mentioned multiple times. Besides the finale for this arc is Zygarde vs Rayquaza and terapagos along with the heroes. Who's to say thats going to end well.
Here's hoping the story follows through with a league or Ace Tournament arc.
Based on objectives, it seems apparent that Liko's primary goal for continuing the adventure is to reunite Terapagos and the Six Heroes to Rakua, while Roy's motive has been to catch Rayquaza and help his starter reach its full potential.
Based on the story's progression, its seems likely that Roy's goals may be fulfilled towards the end of the Rayquaza rising arc, while Liko may likely have fulfilled her goals, perhaps towards the next arc, if its focus on reaching Rakua. All of which may be accomplished near the end of 2025.
If the island of Rakua is not the next arc, then I'd assume the revelation toward the end of the Rayquaza rising arc, would perhaps focus on treasure hunting, in which the RVT are informed that in order to reach Rakua they must retrieve special artifacts, which may introduce the treasure of Ruin legendaries.
If the story were to continue after the RVT reaches Rakua, then my guess would be that the final arc would focus on a tournament arc, to showcase Liko, Roy and Dots growth from completing their adventure.
Based on the content the story has presented so far, there doesn't seem to be much of a reason for why the anime would need to continue the horizon story into 2026.