How much of the world could die without civilization ending?

[Rafael]

So,I was bored at work the other day when someone asked how much, as a percentage, of the world we thought could spontaneously die without humanity basically being rolled into the stone age. The percentage would be evenly spread out throughout the world(as opposed to, say if you said 10% China taking the whole hit). Thought it made for an interesting topic so I thought I'd try it out here.