With 90% 2nd and 3rd degree burns, i don't think he's gonna make it. He'll most likely get a serious infection in a few days, as happens with a lot of seriously burnt people.
re, the plane, BA will get it fixed. Whatever it costs, it'll be a LOT less than a brand new 777. BA have got enough planes for the loss of this plane not to have any affect on other timetables.