A 777 is a monster. It probably can still fly after getting a missile strike. The crew would have gotten off at least a Mayday call.
I'm guessing you missed the part of it being 800 miles. Please tell me any SA missile with an 800 mile range. I'll buy anyone having one. Where is the detection? Is the radar on Mt Everest? The best SA missile the chinks have a 130# + or - warhead which would obliterate an 500 kt target, unfortunately its range in less than 65 miles. In range there wouldn't be nothing from the target especially considering the aerodynamic forces acting upon a body blasted with 130# of HE.