Everyone should bear in mind that Ash isn't the one writing the script making himself an ignorant trainer upon entering a new region. And replacing him wouldn't accomplish what you look for. It would just be a different person then after the next Generation then you have to ask yourself now what? If they have Ash leave then at least progress him.
Also too everyone posting, lets not turn this into another Ash centric topic. The question asks what happens to the ANIME yes that would be the series as a whole not just a single character.