I agree. The way this split breaks down would ensure six liberal Senators. The SF Bay Area needs to be included in the "California" portion, not "Northern California."
That wouldn't happen. San Francisco would never consent to being separated from its suburbs and thrown in with Los Angeles.
But even if it did, Sacramento and the liberal coastal counties would probably give Northern California to the Democrats. There just aren't that many people in inland Northern California.
In a good year, Republicans might be able to elect a governor or senator in the Southern California state, but the other two would be solid Democrat.