If you are asking if it is ethical to delete your own posts that have lost their context, it is to me.
Yes, but how can someone keep track of every post a person made quoting a spam/off-topic (deleted), also keeping in mind if there are multiple quoted posts and single one out of all gets deleted for being off-topic/spam. Then how will the person keep noticing this?, In Hot-Topics moderators can be responsible, but how can a handful mods will ask the poster(s) to delete multiple posts.
I've never heard of this happening before, and as to your question here....there's no way in hell the mods are going to be focusing on 'air-hanging posts'. At least I hope not, because those are trivial compared to the constant avalanches of diarrhea in the form of posts, AI-generated or not, and all the other stuff that shady members pull on an hourly basis.
Also, I could swear that in the past if mods took notice of posts like the one you're referring to, they'd just delete them themselves and the member whose post is flapping in the air wouldn't get a notification via PM, but the offending member would. Maybe things have changed in the past couple of years and I've not noticed. Quite possible.