I was in a similar situation, London to Beijing earlier this week. Rerouted on to Air China direct, on a fairly quiet flight (easily less than 100 pax on an A330). Miles have been credited in CA Y class, which is 100%. It is a few less miles than going via Copenhagen, but these miles have requalified me for Gold for another year so I'm not minded to ask for ORC. I did however have the same fear that I'd be rerouted on a non-Star carrier, on on a Star carrier in a low fare bucket and thus need to push for ORC. By the way I can't praise enough how the Heathrow agents from Swissport handled it.
My only other reference points have been claiming ORC in Mileage Plus (UA scheme) when both Lufthansa and United have moved me to non-Star carriers, which United did. Maybe not getting ORC is the [worthwhile?] we pay for an otherwise good FFP with Aegean.....