Is it a useful tag? It strikes me as a prime candidate for burnination. It's attached to 54 questions, so an edit spree seems like a bad idea here.
Do we need this tag?
I can't imagine a scenario of anyone following either tag in an effort to find questions that they can answer, nor do I think either tag is useful from a perspective of "I want to ignore questions of this type".
If people are not wanting to hear about endings, they probably don't want to hear about spoilers in general. If they're having issues "beating the end guy", then I think they've mis-labled a question entirely.
story items aren't something I can conceive of many people ignoring as well. In addition, I don't think story is needed as a way to quickly identify the type of question being asked. That's pretty self-evident from the title of those kinds of questions.
I think the "I have a question about this game's ending" type endings questions falls squarely into the broader category of story, and there's not enough granularity to warrant the former, given the existence of the latter.
Unless anyone has a better idea, I have no problem merging them, and removing the remainder.
The only semi-valid use of the endings tag that I can imagine would be if someone mistakenly used it as a synonym for "late-game", such as:
Only 40 seconds left in the game, but Tibbers is guarding the Nexus...should I push?
I vote for remove.