The problem with Ziva becoming a full fledged NCIS agent is her nationality. Now, the writers may not be picky about it and that is fine for the show, but I would think with a US investigative agency, one would need to be a US citizen.
Today I envisioned her being fast-tracked toward that goal and having to go through the agency application process, though being asked to teach all the courses rather than take them. LOL. Then she would be the probie and Timmy would be off the hook. However, I don't think there will be any of that, and she will retain her badge while her ties to Mossad are severed. She is home, after all.