User blog comment:SniperGhost/Gulliman's Return/@comment-25033299-20111021154923/@comment-1932673-20111021191817

Plus this and the Serathi are agents of order, acts of order MUST be balanced by acts of disorder, so the more powerful the Imperium and Serathi get, the more influence chaos gains. The imperium will be locked in an eternity of war with Serathi, war is the ultimate form of Chaos, so therefore it would be completely unfeasible to keep Chaos as reduced as it currently is. A Primarch must lead Chaos to reflect this, no soul is safe from Chaos once that individual has perished. The warp isn't called the sea of souls for nothing, Chaos can restore and corrupt Gulliman without being unfeasible. Gulliman's death by the Serathi and the continued loyalty of the legions are all acts of order, they must be counter balanced with disorder, Gulliman must return, look what happened to Horus, it wouldn't be a far stretch to bring gulliman back, only chaos can restore life, for life IS chaos, therefore the mere act of resurrectiing Gulliman would corrupt him.