I fully disagree with that notion, I do not feel serious and compelling stories require character deaths, there are so many ways to add weight to a story without having to kill someone off to quickly gain it.
Rather than having someone die and then everyone react to that, having that be the seriousness and the weight you can just as easily have them react to the horror of the event.
Having a villain come, devastate the party, bring them to the brink without them being able to do a thing, all of them forced to stare at their own mortality while they can do nothing to protect themselves or their friends.
Can be just as compelling as villain comes, kills X and now everyone is sad.

An ongoing plot like 14 can certainly function without killing off the main cast, using Game of Thrones, as an example, why me and some others I spoke with couldn't get into it is some of us use other characters as our vehicle for the story and not everyone is fond of changing cars every few miles down the road when our currently one inexplicably bursts into flames for the tenth time.

I don't think death shouldn't be used or can't be, I'm simply not a fan and feel it's something that can be done, not something that needs to be done.
Using FFX again, it's ending is gut punching but I feel it could have elicited different but equally as powerful emotions if things played out differently, conversely FFX-2's good ending is right up my ally and I feel was just as impactful and meaningful.
Good writing makes a good death, a good death dose not make good writing and good writing can be good, serious and compelling without death.