Ok Thanks.

So to clarify. Because this is a one-way ticket, its refundable up-to the time when check-in cuts off at the point of embarkation (YVR)?

Not quite, you're conflating ticket and reservation. Findark's point about auto-cancellation was just the reservation, that typically happens at the check-in deadline if you're not checked in, or when boarding ends if you are checked in and don't board.
The ticket is completely separate.
Assuming there is no language in the detailed fare rules ("penalties" section) saying you have to cancel before departure (see * below), then you can choose to refund the ticket at any point within its validity (generally 1 year from date of purchase).
But definitely read the fare rules.

*This is language that requires you to actively cancel your reservation before the departure time of the flight in order to retain the ticket value. It is typical for nonrefundable fares but it's always possible a refundable fare has something similar. The auto-cancellation discussed above wouldn't be relevant.
NOTE - TICKET IS NON-REFUNDABLE AND HAS NO REMAINING VALUE IN CASE OF NO-SHOW

Specifically, here is the current Penalties section of fare rules for UK origin refundable DL fares to US/Canada.

https://cimg8.ibsrv.net/gimg/www.fly...51a4e0729f.png

While US/Canada origin refundable DL fares to the UK just say the following with no restrictions. The "CANCELLATIONS PERMITTED" language is airline fare rules speak for refundable fares. While not obvious that is what this language means, it is in fact, the only indicator in the fare rules that a fare is refundable. Note that when you book a roundtrip from US/Canada to UK, both outbound and return fares will use US/Canada origin fares (they do not mix different origin fares when making roundtrip bookings).

https://cimg2.ibsrv.net/gimg/www.fly...7b9838d169.png

Thanks for these extremely informative responses, but as of last night, it's probably moot (until next time). AC and pilots tentatively settled and so unless something unforeseen happens I'll be flying AC and cancelling my DL ticket at least a week ahead of departure.

Thanks again.

I assume you were just sharing that as a point of information as OP is originating in US/Canada? But it is interesting that while the ticket becomes non-refundable due to no-show, it does NOT say that it loses value (like a non-refundable fare ex-US), so presumably you can still re-book if you no-show on a refundable fare on this type of ticket.

Regardless, it's always a good idea to read the Penalties and Voluntary Changes sections of the fare rules, and more importantly, PDF/save them.