Offloading yourself from 2nd segment of an award
 

Due to unpredictable circumstances I may have to change onward plans when I arrive at HKG on a one-way LAX-HKG-SIN award ticket.

I may have to stay on in HKG and abandon HKG-SIN leg, or buy a seat to another destination. It's a long story...

Obviously I could just fail to board the HKG-SIN leg, but I'd rather do the right thing and let Cathay know I won't be flying.

Would there be any problem with that?

Why don't you just change the HKG-SIN sector to another date? You can make changes on Asia Miles. Unless of course its not an Asia Miles ticket.. then yes, you should call CX out of common courtesy to advise that you won't be boarding that flight.

If OP originally had HKG issued as a transit (X), this will constitute a re-route and OP will face change fee and HKG tax.

tell them you wont be boarding HKG-SIn upon arrival of HK (at transfer desk is OK). and at LAX tell them to put you through to HK only n u'll do the checkin there in HK (if they do ask tell them you have private matters and is not sure if you can go to SIN).

Yeah but if you do not intend to the SIN leg than yeah call CX to let them know

Hi thanks for the tips.

This is a AA award ticket.

I dont care about losing the sgement.

The trouble is, I won't really know until I get to HKG what to do, because I'm depending on some last minute information.

I won't have any checked bags, so I think if I find out I'm not going to SIN, I will just find a CX transfer desk and let them know not to waste time paging me for boarding.

Effective Feb this year, AA does not penalize you if you have to cancel the last segment of your itinerary when such change does NOT change the award nature.

In this case, it wouldn't because it is still a NA to Asia 2 award whether it is to HKG or to SIN.

If you cannot know until the very last minute, then do as you plan.

Does anyone know under the same scenario but with BA instead of AA?

You have to ask in BA forum. It goes without saying that BA rules dont equate to AA rules so what AA allows means nothing if you are using BA miles.