Wow, that is a lot of withdrawals, more than I originally thought
It is a shame, as LGW is a great airport to travel through and use.
Whilst I agree with you that we may not see the level of Asian destinations LGW had leading up to 2019, I do think there is scope for some of these carriers to reinstate services from LGW going forward.
Cathay Pacific- Although their presence in London is significantly down on pre-covid levels now, I do think that there is potential for them to return to LGW. I say this because with 80% slot utilisation rules now being reinstated, they are in serious danger of losing a sizeable chunk of their slots at LHR to another carrier if they do not use these slots now/medium term. With that in mind, this will prove to become a big problem for CX going into the medium-long term if they wish to expand their London-Hong Kong services once more, and LHR slots are unavailable. So LGW in that instance would be the next best thing for Cathay if they wish to increase London frequencies, although there is a strong argument that LGW may act merely as a waiting room for them initially while they wait to consolidate all frequencies at LHR. Should there be enough demand in the future, maybe CX would wish to have a dual-London operation once again, in which case, a daily LGW-HKG flight could be sustained alongside LHR. What is also clear was that LGW had been working well for them prior Covid, with the service jumping to daily fairly quickly, and I do remember the CX ground teams in LGW frequently commenting it had grown into one of the better performing "new" routes for the airline that worked well alongside LHR. The A359 was a great fit for this route, so hopefully we will see them back at Gatwick.
Air Asia X - Already rumoured and discussed in this and other threads. The airline has supposedly secured daily slots at LGW for W22, so I'm reasonably confident they will make a return to LGW over STN. I also didn't realise MH had previously operated into LGW?
Garuda Indonesia - Doubtful, but possible if they decide to have another go at London. Routing would more likely be redirected to Bali over Jakarta, given Bali's popularity as a tourist destination. That being said, the airline has tried and failed with both LGW and LHR previously, so I'm unsure if they'd be willing to take the risk again. The only way I could see them re-entering LGW would be to reinstate the tag-on from AMS, but again, that's a big if.
Air China- Possible further down the line, if excess capacity is needed which LHR alone cannot support, similar to their dual-London operation pre-Covid
China Eastern Airlines - Similar to above, would likely only reopen LGW if excess capacity is needed.
Also, I am wondering whether BA might be willing to give LGW another look if they were to reinstate their BKK service, now that Scoot are withdrawing? This carries a lot of O&D traffic when compared to their HKG and SIN routes, so might be a better fit for Gatwick over Heathrow?