I think the question of suddenness vs a slower passing is very much to do with general state of affairs. Are there people dependent? Are there a lot of open threads which need some confusion? Is it below the average age (not that it should matter)? Or are they enjoying their life, perhaps in comfortable retirement?
The passing of a parent would be traumatic in nearly all cases? Can the pain (of an extended illness) be reduced? Or the chaos of a sudden death?