Question A: What happens when an unconscious creature fails their saving through against a banshee?
Question B: Can an unconscious PC hear you?
Let us examine these questions according to the three Duplicate Criteria.
It's the same question, or Question A is already covered obviously as a subset of Question B. Obvious here means I can tell at a glance it's there.
I assert that we have a case of obvious coverage of A by B. Let's review.
Question A states in the question body "All other creatures within 30 feet of her that can hear her", then goes on to ask if unconscious creatures are affected by the ability in question, that is, can unconscious creatures hear the banshee. Question B asks if unconscious creatures can hear. Question A is very obviously a subcase of Question B.
Question B has an obvious answer to Question A. Obvious here means I get a straightforward answer without hard searching — a couple of sentences buried in the middle of a post, or an answer which only sort of implies an answer to Question A, doesn't count as obvious.
Question B is answered by quoting:
An unconscious creature is incapacitated (see the condition), can't move or speak, and is unaware of its surroundings
Question A is answered by quoting:
An unconscious creature is incapacitated, can't move or speak, and is unaware of its surroundings
Question A is answered by repeating back something stated in the question body then giving back the exact same answer as the answer given to Question B.
There is not some strong compelling reason to covering Question A alone, separately from Question B. (If the above bullet points are met this rarely happens.)
OP stated in a comment, responding to allegations of duplicature:
I understand what that other question is about, this isn't a dupe of that. Actually, this question was just that I'd missed the "that can hear her" part of the Wail description, but now that's been pointed out to me, I understand the implications. I would have deleted this question once that had been pointed out to me but that's not fair on the answerer.
OP has stated that deletion would be preferable had the question not received a highly upvoted answer by a new user. This is a compelling reason not to delete the question entirely, and an equally compelling reason to close the question. Mark it as a dupe and set the new contributor's answer as the only answer.
There is no compelling reason to leave the question open in light the first two points I've cited and OP's own admission that deletion would be preferable were it not for the contribution by a new user.
Criteria 1 and 2 are the reasons I initially dupe-hammered the question, but the information revealed in OP's responding comment solidified Criterion 3 in my mind.