I seriously dunno about genuine trauma and character death... because it's such a purely fandomish issue. I've never heard (extreme examples aside) of anyone getting traumatised over this while reading novels, or watching TV or movies... No one ever, as far as I know, suggested something like prologue or opening credits warnings even in works where the main protagonist dies at the end. I can't help but find it very strange that in fandom it's somehow a big deal, but people seem to handle it just fine anywhere else.

Though of course it's possible that those read the reviews of everything they expose themselves to very carefully in advance? Or read the last pages in the bookshop just to make sure?