I think I remember there will be 22-23 books. But if that includes the BAT, I'm not so sure. Also I'm not sure if Battle Ground counts as one of the planned books, or if it adds one to the count, because as I have understood, it was supposed to be the final part of Peace Talks, but the book got too long and had to be splitted and supposedly rewritten to become two separate books.
But maybe someone who knows better reads this and corrects me.
Personally, I want it to end as long as it is still good, if you know what I mean. This is a series, I have never found anywhere else, with so many books and an ongoing story line, that is still really really well written. It even got better, IMHO.
Most long lasting book series start to repeat themselves or get boring or stagnate, because the main character never evolves and never changes.
That's one of the things I like about the DF. You literally read about Harry as he is aging and changing and has to adapt to new situations and knowledge. And he makes mistakes. And although there are several other characters, each of them has a different personality. And you can both laugh and cry while reading. Even if the story line is sometimes sad or very dramatic things happen, there is still jokes and fun in between.
I hope the books continue in this kind of quality. So they are fun to read and re-read.
There is saying here, that you should stop when it is still good.
Because otherwise it will be remembered as the thing that started out awesome and ended boring. That would be sad.