I’ve also heard of airlines canceling “overlapping” tickets which would not be possible unless you skipped a leg. I’ve been hit by that when trying to book multiple flights for a business trip where I didn’t know exactly when I would be coming back, and the advance fare ticket was a small fraction of the cost of a refundable ticket.
Complaining that a customer skips a final segment on the return flight is poor sport. Except for one thing — if they have you in the system because you started your return flight earlier in the day, and now at your connecting flight they are calling final boarding again and again waiting for a passenger that never shows, it holds up the entire plane and is a drag on their resources trying to page you and track you down.
I can understand airlines refusing future service to someone who does this to them repeatedly. A 5 year ban or terminating their frequent flier account or something along that lines would seem appropriate.
The ban might be hard to enforce however since it’s not like Amazon where they can blacklist your address.