Forget Ahsoka, I just want to see these two get killed, since they do not "exist" as of ROTS:
1) Asajj Ventress
2) Cad Bane
Huh? Why don't they exist in ROTS? Because they weren't mentioned? That's a really literal way to look at fiction. Endor wasn't mentioned, but it exists...Hoth wasn't mentioned, but it exists...Sandcrawlers weren't mentioned, but they exist...Han Solo wasn't mentioned, but he exists...We didn't see Dodonna in ESB, but he existed...we didn't see the Kubaz spy in ROTJ, but he existed...and so on...
If you saw a movie about the U.S. Civil War, and they never mentioned Japan once, would you assume that Japan doesn't exist?
Anyway, about Ashoka...I don't think they will kill her. She's become too popular and a symbol of girl power in the geek community.
I think she will be sent away, or run away at one point. In fact, I think that Ashoka could return as a focus of more SW entertainment.
Who knows? Maybe she's on that Outward Bound ship in the Thrawn Series...