No.
My personal opinion is that nothing would actually change. You'd get some other noob trainer at the start who eventually does well in the championship tournament only to forget everything and revert back to the status of noob when he starts another region. I mean that's unless they change the main protaganist at the end of every region (then that'll be too much change and people would be moaning about that). It's a problem with the nature of the show, not the charachters.
I would definately stop watching the show if Ash left. As I've said I don't enjoy the show on a intellectual or dramatic level - the only reason I watch is to find out what happens to that young trainer I first met 11 years ago. He's an ambassador of the show and he means a lot to a lot of fans.
Either way there would be people complaining about the show if Ash did leave and a new guy (assuming a male, don't know why I'm being sexist) came in, "he's does't do this", "Ash used to do things this way", "He's boring" etc etc. It's a no win for the writers.
"You can please some of the people all of the time, you can please all of the people some of the time, but you can't please all of the people all of the time". John Lydgate