[quote]"A few were spared. Some adopted new strategies for survival; they went dormant. Others became dust that could regenerate our past forms; time rendered this dust defective. It brought only disease and misery; but that was good, we saw the misery and found it good."[/quote] This is from page 174 of Silentium. Basically, the Precursors did become dust, but the dust was eventually corrupted and instead of regenerating the Precursors, it created the Flood instead. And the Precursors, in their insane lust for revenge, used it to attack and nearly destroy the Forerunner empire and the entire galaxy.