Translation Question from Harry Potter and the Philosopher's Stone


I have a question about the translation of this sentence from uncle Vernon in
Harry Potter and the Philosopher's Stone:

Original Japanese: "あいつらは身から出た錆、魔法使いなんて変な仲間と交わるからだ …
**思ったとおり、常々ろくな死に方はせんと思っておったわ** "

My translation: "They got what they deserved, because they got involved with
those 'wizard' weirdos... **Just as I thought, I thought there isn't
always/usually a good/decent/satisfactory way of dying**."

Published English translation: "Just what I expected, always knew they'd come
to a sticky end."

I don't quite understand how the text in bold comes together here to form the
intended meaning. I'm not looking for a smooth translation, rather just trying
to grasp how the Japanese comes together here.

Many thanks in advance.




It parses as:

` ╔ 常々 ║ ╔ ろく-な ║ ╔╩═ 死に方-は ╠═╩═══ せん-と ╚ 思っておったわ `

Or, in standard Japanese:

` ╔ 常々 ║ ╔ ろく-な ║ ╔╩═ 死に方-は ╠═╩═══ しない-と ╚ 思っていたぞ `

Going outside in:

  * "常々 **X** と思っておったわ" = "I've always thought that **X** ". 
    * What was X they always thought? That " **Y** はせん" (= " **Y** はしない"). This means "as for Y, they won't do"; it's an emphatic way of saying "they won't Y". 
      * What is Y that they won't do? To die in a decent way ろくな死に方。
  * Putting it all back together: I've always known that they'd have no such thing as a decent death. 

