At Celebration this year Dave Filoni revealed they had already worked out how to end The Clone Wars. It was to continue into the events of ROTS.
Sounded to me like they were planning on only going to season 8 or possibly just a full season 7. So they got cut off right as they were winding down. Which is why I'd still like to see them finish what they had started. (Bonus: Ahsoka leaving the order wasn't supposed to be her departure from the series)