Excuse me, guys, this isn't going to lead anywhere, and it's also not what I asked about. I don't think either of you is going to convince the other side otherwise.

Assuming that this is a bit like not using all segments of a flight booking, Italian courts have ruled that cancelling tickets due to a no-show for the first segment is illegal.
Lufthansa lost in court after trying to charge a German passenger extra for not using the last segments of his booking.
Meanwhile, courts in other jurisdictions may come to different conclusions, so I suggest we just agree that it's not 100% clear.