I am booked LGW-HKG-SIN then ICN-HKG-LGW a few days later all in PEcon or Econ

Having been injured, I want to upgrade the LGW-HKG at least to J (flat bed).
I found out the price was so high (about $7000 USD) that it is better to pay about $2200 to go J on Malaysian Airlines LHR-KUL-SIN BUT BUT BUT ...
I assume that if I don't fly LGW-HKG-SIN the rest of my ticket will be cancelled... Is that right?

Any chance of an airport upgrade on arrival at LGW?

I don't think CX do airport upgrade promotion anymore but I am sure you can pay the change fee and fare difference to upgrade.

Since you no showed first leg the rest would be automatically cancelled unless you speak to CS to protect your segments. You may be charged a no show fee.

Do you have insurance? Amex Platinum for example covers this I am certain.

From my personal experience CX ground staff are quite nice in rebooting, especially if you are DM or OWE.

Thanks for sharing your experience. I am OWE. I will phone them and ask about segment protection. I made the mistake of booking via ebookers who don't seem geared up for handling slightly off beam anomalies - although the staff are polite!

Thanks.

Any extra cost should be paid by the car driver (insurer) who knocked me off my bike, but cash will be a long time coming!

You will NOT be protected. Because basically you are changing your return ticket from LGW-SIN//ICN-LGW to just ICN-LGW. So basically you will need to cancel and refund your entire ticket and buy a separate one way from ICN to LGW.

Check CX website POS in ICN, you might find a good oneway fare in Business.

Yea, to second what Guy Betsy implies...

This is not a "slightly off beam anomaly".....this is basically like the cardinal sin #1 of etickets, unfortunately. You absolutely should get CX on the horn, and I expect at the most what they'll do is allow you to cancel without penalty if it applied. You just are not going to be allowed to start a ticket halfway through. This eliminates the whole crux of point of sale pricing discrimination, despite the unfortunate situation you have been placed in.

Now, that being said there's a decent chance an ex ICN biz pricing will be attractive like said above. But I just wouldn't get your hopes up for CX to allow you to run the second half of an itinerary and not the first. We've got threads on here where CX doesn't allow that for funerals let alone an injury.

I suspect you have some work to do.