The Elder Demon's Dilemma — G. Akella

The ninth and final book in the Realm of Arkon series.  

The world stands on the edge as the Ancient Gods advance on the Great Forest. An enemy from a past life aims to transform into a Beast and destroy Providence itself....

To stop him, all must stake their life on the Scales of Fate. All must make a choice, THE choice. Death in battle or life in slavery. A beautiful demoness' smile or the eternal, infinite Void.