What we do with dead still-open questions?
By dead I mean that the OP had not return to Arduino SE for over a year (and probably will never come back), and therefore the question will be never closed, even if it had acceptable answers posted.
I don't think that you necessarily mean closed but rather has an accepted answer, and as such, is thus removed from the list of unanswered questions. I noticed such a question yesterday: HC-12 with Arduino Mega.
It is a reasonably presented question, with code and a schematic, and it seems as if the user had found a solution. However, an answer was never posted, and even though a suitable answer could be extracted from the comments (see What if a comment solve the question?), the OP may never return to mark it as accepted and therefore remove the question from the unanswered list of questions.
Another example, but where there is already an answer, is How to get the server response when I post to a web api
There was a meta question (to which Nick gave an answer to) about having moderators marking an answer which is an obvious solution to a question, as the accepted answer, see Questions with good answers but none accepted.