So this is a hypothetical question and the DONEx has not actually been bought yet (JL cannot be included on OWE yet, so you cannot buy this ticket before April 1). Might I suggest that you route LHR-HKG-DPS on CX instead? Much nicer flight than JL (which runs a stripped-down J for DPS, don't expect the same J you would get LHR-NRT on JL, for example), and HKG is far nicer than NRT for connections. And CX at LHR could retag your baggage through to DPS if it was only able to be tagged through to HKG; or accept check-in 9 hours before (unlike BA). This would save you the left luggage fee at LHR (which is pretty high, something like USD 20 per day when I last used it).