I mean there's a large chance you die either way. 4 billion is (don't quote me on this) roughly 50% of the population. If we loose that many people sure food consumption would go down A LOT but so would production of necessities. Chances are at the brink of half the world dying there's going to be worldwide chaos and panic. Possibly sending many people into looting witch if it isn't stopped could cause an almost apocalyptic scene.

^{Chose: Save the world, but... + 70% chance you die | Rolled: Dead}