I understand why they killed Joko but he was an interesting character. There is a way they could bring him back with restrictions. As far as I'm aware they never explained the origin of the djinns. They could bring Joko back as a djinn. The djinn look like awakened so it's possible they are what happens to powerful undead lich when their bodies are destroyed. A djinn Joko could be bonded to the place where he was destroyed or he could be part of what is making Aurene tired. She could cough him up as a djinn bonding him to that location.