What matters is whether the character (Neelix) is affected in any significant way by this major event (as any normal person would be). It could take the form of PTSD, or another form, just something that communicates to the audience that these are real people (within the universe of the show), and not Sesame Street characters.
I think it was actually a better idea to have Neelix be the one who suffered the missing lung and the repercussions of it (which my other post mentioned, it does change him for the better) than some random red-shirt ensign. If there was one problem with TOS, its that no one gave a shit every time a red-shirt kicked the bucket.
Voyager has plenty of examples of random "red-shirts" getting killed off, when I would much rather they have used an established character. Killing someone we already know and love conveys the magnitude of their situation (think, Tasha Yar in Skin of Evil
. Holy shit, that mud monster just killed Yar! He's evil!!!!!!)