I believe Qantas still hold four slot pairs at LHR. There's no chance of them starting LGW. I can't see them ditching LHR-SIN either - there's enough local traffic at both ends, as well as connections to BNE. LHR-SYD is also going to have awkward timings due to the curfews at either end, so there would be plenty of passengers who will stick with the current one stop service with it's present timings.
UA maybe, DL to BOS maybe. Riyadh Air possibly. GA no chance, HK Airlines no chance, Azul no chance. African routes by previously mentioned "national" airlines far more likely.