BEWARE however, that they most likely will cancel your return flight.
Not "most likely," but "WILL." And then you'll be stuck, since the carrier's published tariff indicates that failure to use one segment entitles them to not only cancel your downline space, but you'll be required to requalify for a brand new fare as well.
Point being that some agents will gladly search for less expensive fares, which would in this case be SEA/DEN/SEA. Do you have any idea as to how many different fare structures there are?
Yes, but they can only sell you what you actually plan to fly. Air carriers view back-to-back, hidden city ticketing, and other creative ways of circumventing fare rules as theft. Agents who are caught intentionally booking customers on these creative routings are subject to disciplinary action up to and including discharge.
And yes, genius...as an airline reservations supervisor, I DO know how many different types of fare structures there are.
"In this present crisis, government is not the solution to our problem - government IS the problem." - Ronald Reagan
Comments made here are my own and are not intended to represent the official position of Alaska Air Group