Yes, it is time for the TV show Nikita to end, because the show is past its prime. A show should always go out on top, like Jerry Seinfeld did. Nikita has dragged on and people are no longer interested in watching it. Developers should put their time and energies to work on a different show.
The conclusion of the show cannot be achieved in one 40 minute episode and therefore should be extended so as to allow viewers the appropriate amount of time to adjust to the end of the era. The single episode provided for Nikita an Alex to right the world is not sufficient to tie up all of the loose ends regarding the many necessary characters.