If you no show for the return, it will be cancelled and will retain whatever value it has under its fare rules. That is most likely $0. Thus, the end result is that you lose the value of the segment(s) in question and would have to purchase a new ticket at whatever the prevailing prices are at a later time.

In the current environment, you might want to check on whether you can have a fee-free change to a later date when you might use the segment.