Surprise! I found out (at the airport, trying to fly home a few days later) that because I hadn’t boarded the first flight, the airline had resold my seat on the return flight. I was not credited for the seat on the return flight (which was now unavailable to me). I wasn’t even notified that it was forfeited when my trip was cancelled. Pressed for time, I had to purchase an additional one-way ticket home.
I understand the motivation to resell an unused seat at flight time in the event of a no-show. This, however, struck me as a deliberate predatory theft of my reservation, a sort of loophole to deprive me of my reservation without recompense. I don’t think a scenario such as this is unforeseen by the airline (an honest misunderstanding); rather, I think it is exploited.
The airline may have a clause somewhere on their website explaining that the above is to be expected. That doesn’t make it square for me. The behavior of the airline was, IMO, unethical. If I ever face a similar scenario in the future, I will know to communicate explicitly with the airline about my intention to use my return ticket. However, I shouldn’t have to do so or risk finding myself stranded away from home.