If you want to tell a story about the end, about despair and about hope in spite of it all, what you need to do is you need to make these concepts resonate at every level. You can have big universal concepts like the fate of the other stars and dynamis and all that crap. But you need to make it resonate at a personal, character level as well.
The question the Endwalker story should have tried to induce in the players is: With everything that happened, why should we go on? And not on a meta level (why should we go on if the story is so shit?).
There is in my opinion no substitute for character death when it comes to finality, for left regrets, things unsaid, for fate inescapable, death is the ultimate end and thus should have been a major part of Endwalker. Imagine if Alphy had died and his dad had just MISSED the chance to tell him what his son really meant to him? THAT is despair. Imagine Alisaie giving Zenos her bit of advice as a consequence of her having grown BEYOND revenge and seeing him for the pitiable bum he really is? That is someone who is able to move on in spite of it all. Isn't this what Endwalker was going for thematically? They could have gone in a fantastic direction with all this.
Also, imagine a main character dying in future expansions. Endwalker was the perfect place for it, I just can't see it happen in a satisfying way anymore, it would rehash the theme of Endwalker better than Endwalker. Satisfying in a horror kind of way, I don't enjoy characters dying in a sadistic fashion of course.
All that said the Urianger quest on the moon was great tho.