I bought a ticket in M class econony standard for 10,000 hkd, ticket expire dec 30, 2015 (I already flew the first leg)
There is a high probability that I cant use the second leg by dec 30 but I need the same flights for Jan 30, 2016.

Below is the fare rules
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Rebooking

Free of Charge. Fare difference may apply
Cancellation Fee

Before departure: TWD2400
After departure: TWD2400
Stopover

Stopover Hong Kong:
2 stop(s) permitted. On the outbound journey free of charge. On the return journey free of charge.
Note

There may be other charges associated with stopover ie. Taxes.
Stopovers must be "en route" during the journey; conditions from the fare rules apply.
Mileage Accrual

You can accrue Asia Miles on this fare.
Upgrade with Miles

Permitted
Pre-book Seat

Permitted
No Show Charge

If you do not turn up for your flight there is no penalty

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What are my options?

Should i pay TWD 2400 and get a refund? If i do opt for this option would my refund by 5,000hkd or something less?

Can I upgrade to H class and extend the ticket for another half a year say June 30, 2016? or to J or PEY so long as i can extend the ticket by 1 month

Yes you can extend the ticket to a higher fare with a longer validity. You can extend if the rules allow you to combine the different fare classes, otherwise CX will price it as a complete H or higher fare. I don't know what you bought so you'd have to ask CX what your options are.

RTs on CX are discounted heavily (but not OWs). So do not expect much for a refund.

Which route is this? Just TW-HKG?

Jan 30 travel is definitely inching close to CNY....

travel is khh-hkg-jnb-cpt round trip, repositioning for a rtw in cpt

I think you will be able to upfare, however, you would have to pay the fare difference for the entire round trip, since the most restrict fare rules apply on round trip tickets

Thanks guys I will give CX a call

Okay so first I thought you were just delaying the inbound. (You are starting a RTW in CPT, returning to CPT, then come back to KHH.) If that were the case, the following information applies:

Yes, for ex-Taiwan CX tickets to South Africa, M class is 6-month validity. You can upgrade to K class (need to be for both outbound and inbound) to extend the ticket to 1-year validity. I'm guessing you departed on 30JUN2015. If that is the case, you would prolly end up paying the fare difference should be 4500TWD plus the change fee 1500TWD, a total of 6000TWD, providing that K class availability exists for the inbound.

If you mean you want to change this to a oneworld explorer or global explorer, it might not work. The RTW fares book into L class, but you already took the outbound in M class, which is higher than L class. I don't think CX will allow you to change a M class ticket to a L class ticket. Not sure about changing it to a Business class RTW.

While you are supposed to fly all segments of a RTW trip, can you pass through KHH or TPE and end your trip there instead?