I doubt they'd kill off Ahsoka while the show's still in production. After all, she's the only lead character whose future isn't dictated by ROTS, so she's the only one that can have any real growth or change in her character arc. They'd be fools to give that up. Heck, that's no doubt why they created her in the first place.
For that matter, Ahsoka's the character who's played the largest role in the current season. There have been five 4-part arcs this season: Onderon, the younglings, D-Squad, Maul/Mandalore, and the current Jedi-traitor arc. And Ahsoka's been a central character in three of those arcs, more than Anakin or Obi-Wan. By this point, Ahsoka is effectively the star of the show. Now, one could argue that they're just featuring her so heavily because they know she's about to go out, but I don't think that'll be the case, for the reasons I gave above.