In that situation, I would either employ the explosives I am no doubt carrying(armed and ready), of course I would probably smile at him and say one word before detonating my explosives, that word, in my best "Demo man" voice "KABOOM!".
That or if by "Save the world" you mean, "Liberate it from the tyrany of it's current overlords" I would just yell "flubberpickle" and cause the subdermal implants I put into him and his closest comrades to release a combination of nerve gas(directly into the lungs) and sidney funnel web spider venom(straight to the heart, or the closest artery leading to it.)
and spend the last few moments of my life watching them drown on their own blood and saliva whilst they experience the highest degree of physical agony known to man, then awhile later, when my beacon is followed by loyal followers, be reborn in a machine, my brain implanted in a robotic body with systems to sustain it's functions nigh infinitely.
After all, we are talking about a completely hypothetical situation, and thus fictional outcomes are allowed, yes?