Helpfully, we've got an objective frame of reference available: the system automatically deletes questions under certain conditions. I'll summarise the points relevant to this discussion (leaving aside spam etc), but you can find the full details at that link under the "By the system" heading.
A question gets deleted if it is unlocked and meets one of these criteria (these checks are made continuously):
- The question's closed (not as a duplicate), has zero or negative score, it has no upvoted or accepted answers, it has no pending reopen votes, and it was closed over 9 days ago and hasn't been edited in the past 9 days.
- After 30 days: The question has no answers and a negative score.
- After 1 year: The question has no answers, a score of 0 (or 1 if the user's deleted), very few views, and 1 or no comments.
This is our baseline. These exclude anything with a mere score of 1 (bar deleted authors), and anything that's answered, because answers can be useful to someone, and I will almost never vote to delete a question that has worthwhile answers. We humans have the delete privilege to be intelligent (unlike a bot!) and delete the other stuff that also isn't redeeming.
Despite the generous criteria, our delete-bot deletes quite a lot of questions. This includes questions which could maybe be reopened if they were edited into something different.
Our guidance isn't meant to be as generous as erring on deleting almost nothing, or even reserving deletion for absolute garbage or off-topic questions. It's just: keep stuff that has some genuinely useful content that people actually care about, and delete the rest.
If you want a question to stick around and it could be something useful, edit it.
Or don't, and let it get deleted, which I think is actually doing people a favour: if it's an important and good question, someone else is going to have it, and at that point, we get to have someone asking a genuine question with a real problem they're actually facing, instead of an artificial attempt to preserve a question made by someone who isn't actually facing that problem. Those artificial questions are generally inferior to questions by people facing the real issue anyway (as we've just experienced in our very controversial tide of 5e Basic questions).
Even if that's you who's experiencing a problem, and you find a closed question that kind of touches on the problem but does so badly, you're probably better off letting the original get deleted and asking it yourself anew - that way you become the question's custodian, and we have someone active accountable for it. It also means custodianship isn't shoved via an edit on someone else who doesn't care and didn't ask that question and who might be outright unhappy about it.
Questions aren't sacred. There's no inherent reason to save any question under threat of closure or deletion, unless you personally care about it strong enough to do something about it. If you don't care, it has no value to you - leave it to someone else to save. If nobody cares, why would we want to save it?
If it doesn't have any particular value to you and has no answers that could be useful to people, it has no lasting value.