They're not going to get rid of Ash, compared to how other anime franchises like Digimon and Yu-Gi-Oh changed their protagonists before, but they refuse to get rid of Ash because they fear the series will fail if they did, even though the aforementioned franchises didn't fail when they changed their protagonists (and even if it did, it was for entirely different reasons unrelated to the protagonist), and neither has any other long-running anime franchise that has also done this.
This is combined with the fact that Ash's main Pokemon is Pikachu, the mascot of the franchise, and as long as Pikachu is the franchise mascot, Ash isn't going away or anywhere. Even if they got rid of Ash, there's still Pikachu you have to think about, and granted they could have the next protagonist have a Pikachu as his starter, but that's out of the question.