Larksong dies abruptly in Squirrelflight’s Hope from prey sickness (food poisoning). So my reasoning for that in this AU is that he had a primary immune deficiency disease (primary = present at birth) that made him easily susceptible to illnesses, especially respiratory illnesses. (There are a plethora of different primary immunodeficiency types, but those require research and my body and brain are only letting me do the bare minimum at the moment. So his type is not specified.)

Sparkpelt was aware of this, but what was so shocking was how sudden it was. He seemed to be getting better…then he didn’t. Combine that with having just given birth and Sparkpelt was a primordial soup of trauma.