Providing the most accurate answer based on available information
So, after checking sources like Douban and episode summaries, we still don’t have explicit info on the cause of death. Since the character is described as "deceased" but the cause isn’t specified, I’ll relay that information clearly: the cause of death remains unconfirmed, and we can't safely assume details like illness or accident.
Crafting final response based on available information
It seems there’s no clear mention of Bao Xizhi’s cause of death in the available episodes or official materials from TVB. According to Wikipedia, he's confirmed as deceased but with no cause specified. We can only say he’s “已故” and the story may reveal more later. To be accurate, I’ll suggest checking later episodes.
Citing accurate sources
We can reference Wikipedia for confirming Bao Xizhi as the deceased brother (“亡兄”). I'll also cite Douban and TVB for their synopses, which don’t mention his death cause. Additionally, the TVB programme snippet and HK01 recaps don’t provide details either, so I can just mention those without citing them all.