Wraith is out for the week so Blood is in limbo. Dyleon has no fealty to the Death God. Hence his generals have no power over him.
Fun fact, Darko is actually misinformed. The books are at two different locations.
The Volume of Exalted Paragons (The Book of Ultimate Good") is in the Grand Temple of X, I am under the impression we are now attacking what is NOT the Grand Temple, which would be filled with would-be champions of the gods, not to mention attracting major issues. Originally the Grand Temple would be on an island as well... and Well defended. The Smaller Temples of X could be viable for attack. But it is within reason that Darko is misinformed about the location of this book as it is a secret treasure of the Grand Temple.
The Diabolic Folio ("The Book of All Evil") is actually in possession of a Black Moth Warlock. The Black Moths, unlike the White Moths who run the temples of X, are a sect of followers who seek to learn secrets for their own benefit. That being said, anyone can declare themselves to be a Black Moth, but by the nature of the Black Moths, they are a twisted society of schemers and backstabbers who more often work alone to meet their ends. There are some benefits though to being a Black Moth as they may barter and exchange secrets with each other, only to capitalize on them later to glean an advantage against other Black Moths.
It could be possible for Darko to send a general to hunt the Black Moth Warlock down, X does need to reclaim the books from his less moral followers.