What Determines If A Skill Fizzles Out On Death?
Some skills, such as 
W and E, will fizzle out even after they've been cast on death. 
has the same problem on his W and Q.
However, other skills still land / continue despite a champion's death, such as 
's W, 
's Q, etc.
Is this just spaghetti code or is there some rhyme or reason that some skills continue past death? "Skills with a delay" doesn't seem to be an all--encompassing reason, since Vel's W and Kayn's W work in nearly identical ways.
case is pretty simple, the spell doesn't check wether the caster HP is 0 or 100% but merely check its position. Is easier to code that way and creates less lagg when executed (as it has one less check to do) and over all is pretty consistent with abilities that return to the caster as all of them finish their path after death. 
boomerang for example will also return even if ganr dies mid way (although that one returns to a specific point rather than gnar)
will do full damage with her ult when you kill her when you are already on the air. I don't understand why vel E don't persist, that one is the only one that truly seems like it should persist as it is a projectile with some CC attached to it. Similarly Xerath W shoudl still hit while his Q shouldn't.
Q 
Q