The final episode of The Clone Wars features the supposed death of Ahsoka.
Episode VII reveals that she is still in fact alive, and she features breifly in the film.
I would hope not. I don't consider myself a "purist" by any means, but to me the Star Wars saga should only include the official main feature films. The Clone Wars stuff is fun, but I treat that stuff like the EU books. None of which I've read. I don't want to have to sit down and watch hundreds of hours of cartoons and tv shows in order to understand what I'm seeing on the big screen. Much like Star Trek TWOK didn't require me to have seen "Space Seed", I shouldn't have to know who Ahsoka is to understand her role in the film.
Now, a stand alone film featuring Yoda from 1000 years ago is fine by me, as long as its not required viewing to understand the main trilogy of trilogies.