I think, if the reason is not said, it's logical: logically, lucian is dead when he was attacked in the 7 sanctuary. even if he was "save" with the ritual for become the divine, he was "dead" for become the divine. this is why he only reaper few month after the ritual in divine, it's because he was dead.
so we can think that when he "died" he can't leave the hypertomanci plan for the "dead plan" because he have the power of the "divine" who lock this transision.
so in this case, DKS is not impossible
sorry for my english, i'm french so it's possible that i have lot of error of translation
