When I called and asked similar questions to yours a couple of weeks ago, I came away with this understanding from the SWA customer service...
When you book with points and want to change a reservation because the price went down, those extra points that are saved now go back into the pot they came from, no matter whose ticket you purchased with points. When you cancel a point reservation you made with your points for you or anyone else, those points go back into your pot from which they came. As long as you have "new" points earned thru flights or RR partners going into your RR account within a 24 month period, none of the points expire...not even the ones you purchase. If anyone has newer/different information, please share.