Moderator, Iberia Airlines, Airport Lounges, and Ambassador, British Airways Executive Club
Join Date: Feb 2010
Programs: BA Lifetime Gold; Flying Blue Life Platinum; LH Sen.; Hilton Diamond; Kemal Kebabs Prized Customer
Posts: 63,760
I see a distinction between the two parts here. If you cancel the last sector just before departure, and it's the only sector left on the coupon, all the agent will do is refund the taxes (etc), no quibble there. If you do it in advance, that's another matter, you risk a re-price.
The other part is the Hidden City question: if you are going to get done for this, then you will get done. A big "if", about which no-one here can be authoritative. Refunding the taxes may or may not put you higher up the radar screen, but probably it's in the wash.
So personally I would cancel and see if you get a few bob back. However I would never advise anyone to drop the last sector if Hidden City pricing is in effect.