I first wrote this question with a this title :
Why Obi-Wan and Yoda disappears when they dies while Qui-Gon and Vader don't?
Then I step back and reformulated it by replacing the character names with the more generic "Some Jedi" and added spoiler markup in the question text.
The only problem is that I think the new spoiler-less question title would be less reachable though search engines, such as Google, since the first reflex is to use the names of the character in the search query.
So, what should we prioritize: a spoiler free environment or question titles that better match what people with the same question would be searching for?