Some fans have speculated that Ash will no longer be a main character in the Pokémon anime after the current series, Pokémon Journeys: The Series (consisting of seasons 23–25), is over. The last few episodes of the series will be released in Japan in the coming weeks.
This market will resolve positive if and when an episode of Pokémon Journeys: The Series is released in Japan that shows Ash "leaving" the show or otherwise indicates that he won't return as a main character in future series.
TV Tokyo execs have apparently confirmed that Ash will remain involved in the Pokémon anime in some way, but haven't said whether he'll remain a main character. There is said to be an announcement on the live broadcast of the December 2 Pokémon Journeys episode in Japan (which I guess has already happened).