No it's not possible to crossfeed the extinguishers from one wing to the other. It's 2 bottles per wing but just pulling the handle out will close the related engine & spar fuel valves, the bleed valve, trip off the related engine generator, shut off hydraulic fluid and depressurise the engine-driven hydraulic pump so
hopefully that would be all the fires 'fuel' and ignition sources removed.
For fuel burn, a rough estimate is 10 ton per hour with taxi burn of 1500kg per 10 mins. HKG-LDN (Nepal) is GC distance of 1750 so a 744 at LRC should do that in just over 3.5 hours, so add a little for airways and departure from HKG and I think the fuel required would be in the ballpark of 40,000KG plus normal reserves.