Most SWG's shut off when the water temp falls below a certain level, doesn't matter what the salt level is (my Aquarite manual says 55).

As for what to do for winter, the cell should have unions at both ends. I take everything in for the winter here in NY (fillter housing and pump go in the outside shed; filter grids, SWG cell and filter valve go in the basement). All of the electronics stay outside in there weather proof (I hope) boxes.