Correct. It's not possible to selectively cancel legs on an existing ticket to/from MEM. So, front end, you need to re-book which always runs the risk of price difference or non-availability. You'd think cancelling the scheduled ticket would free up that seat for re-purchase but you obviously have to commit to deviating to see if that's the case.

Back end (if pricing or ticket availability were an issue with the deviation ticket), I suppose one could not deviate, use the first leg of the scheduled ticket to their city (no checked bags), tell the company and the airline plans have changed upon arrival and go home.