The gods avoid the abyss and have their powers weakened their as even the souls of their faithful are beyond their reach once in the abyss. This means that something down their can be weaponized into weakening, imprisoning, or killing the gods. Find out what keeps the gods out and you will know their weakness for once. You might think they will smite the demon who did so, but they likely won’t. The gods fear nothing than a lack of followers, however if something could kill them they would likely fear it and wish it destroyed, but as they would never have experienced something such as this before it will likely make them uncomfortable and many might not truly understand the concept of their mortality after having lived their entire lives free of the prospect of death and fear.