The Mage Founder IV: Obliteration (Descendancy of Kiron Book 7) by Andrew Gille

After being killed by Galeon Promos in an Earthly battle, the vile Xorian mage Ashlan Vylnaxx has found new purpose as the Supreme Sorcerer of Hell. Galeon must travel to Hell to stop Vylnaxx from harnessing the power of demons to help aid Machenrauch in bringing his demonic army to Earth. Meanwhile, years of peace explode into war in the Burning Expanse as Galeon’s wife must assume control of the Kormyrithian army to fight a war on two fronts. Illyana and Galeon’s sons Banner and Jadlon must step into leadership roles neither may be ready for as the fate of Kiron hangs on their success.