I'm liking this 'Proclaim we'll ascend him and kill him' plan, and it is similar to some thoughts I've had myself. As an addendum to the plan, another thing we could try is claiming the credit for any longevity: Attempt to take over his narrative of 'Awawawaffle is Immortal' with 'My Chosen People are Immortal.'
We're a death spirit; we can act impressive in a relevant manner. With our fancy new avatar we could show a dramatic sign of our favour next time he holds one of these things and maybe Stave off Death on a few other settlements too, to make sure he isn't an outlier.