California cannot fall into the ocean. Everything in geological nature generally settles at a 45 degree angle and there would need to be a void to fill in order for anything to start moving. A substantial amount of sea floor would have to suddenly move or disappear to make room for the land to have something to fall into. What's more likely is that the faults would separate enough to fill with sea water from one end to the other causing rivers to form separating the state from the mainland but the rivers wouldn't be very big so it wouldn't be seen as California has separated but more like "Oh, great! Now we have to build some more bridges!"