Onward connections or no onward connections from HKG, Cathay are content to channel all their MAN pax through LHR on codeshare BA shuttles. Unfortunately this is unlikely to change in favour of a resumption of CX passenger flights in the near future. But hopefully Oasis Hong Kong might just put HKG back on MAN's departure boards soon fingers crossed as CX almost certainly wont.
Only time recently that CX came close to restarting MAN was a couple of years ago, but they ran a mile when the Moscow stopover fell through.