I've just read that Linda Hamilton has been confirmed for the new Terminator movie.
Hamilton played the role of Sarah Connor in the first two movies in the franchise. The upcoming film will be the sixth.
I don't know how they get around it because, in the third movie, we're told that Connor had passed away.
With that said, they did manage to mess around with the story with the Terminator television show - The Sarah Connor Chronicles - a number of years ago and they did a timeline jump where Connor, her son - John - and a female robot sent from John in the future to protect them managed to skip a timeline.
It was artistic license to get a TV show with Sarah Connor in it and not mess with the story arc from the movies, so I'm not sure how they manage to get her back into the movie canon unless we're supposed to disregard the third to fifth installments.
I would say that having Sarah Connor brought in after being dead since the 2003 movie is a little far-fetched, but so is having Terminators sent from the future to protect a future leader is!