How much of the world could die without civilization ending?

[Rem-13]

I suppose that would depend on what you consider civilization, and the nature of their deaths. The only way I see civilization (as I consider it) being completely stamped out is if you had something along the lines of what happened in A Canticle for Leibowitz, where there was a devastating nuclear war and then a resultant 'anti-intellectual' fervor that actively sought to erase what was left of the past, and I don't see that being realistically (lalz) comprehensive enough. Even if 90% of the world died of a sudden illness there'd be enough infrastructure left so that after the initial deaths that the generations afterward could rebuild (if they survived at all).

Civilization is deeply embedded in our culture, we'd institute it at a local level; tribal and then upwards as population recouped.