For compensation purposes, only if the cancellation happens at < 14 days before departure. Generally such a cancellation would occur >2 months out (schedule firming), or < 2 days out (disruption). It's uncommon for airlines to cancel flights in that 2 days-2 months out period.
Furthermore, IATA rules stipulate that when it is a schedule change (defined as any time change or cancellation occurring > 72 hours before travel), the ticketing carrier is responsible for managing the schedule change. The operating carrier has no right to just simply take over/take control of the QF ticket.
When it is within 72 hours of travel, then a time change/cancellation that occurs within that 72 hour window is defined as a disruption. The operating carrier would have been given control of the ticket coupon at 72 hours before departure and therefore they have the ability to reissue the coupon to whatever they like.
Even in a scenario where AY might be willing to pay for the SEA-DFW/ORD, they would need to take over the affected coupon SEA-HEL and reissue that coupon to be SEA-ORD/DFW and ORD/DFW-HEL. But AY don't have control of that ticket coupon, until 72 hours before departure, so they can't.
Now you might be thinking well this is passenger unfriendly, why can't any carrier that is part of the ticket, reissue the ticket at any time? If this was allowed, tickets would be broken up quite quickly into multiple smaller tickets by the participating carriers on the ticket... and that's when it gets incredibly messy. You would start to lose things like being protected on the same ticket as a through journey amongst other issues.
For example, if you decided on the day due to a major delay you no longer want to travel, and the ticket coupon was taken over by another carrier at some point months ago, good luck getting a refund. It's almost impossible.