That adds more work and doesn't help the moderator.
When a mod sees a dead post, they click one button to mark it and another to send it to the appropriate trash bin. You are suggesting that the moderator adds YET ANOTHER step PLUS have the admin staff create another reaction tag for the benefit of the poster. Again, it is a poster's job to keep an eye on their posts, not the staff's.
Please remember Mods volunteer. It's a thankless job. They do a lot here. Asking them to do more work in the name of helping posters who are unable or unwilling to look after their links is unfair and would make it unlikely to maintain a quality volunteer staff.
If I am speaking out of turn, may they tan my hide. But the truth is, they have enough on their plates without making arrangements (however simple it might be to you to accomplish) that promote lazy posters. Not that YOU ARE one. But others would NEVER
EVER look after their own contributions if this were implemented.
This is why creating policy that alerts a poster of their dead links is never done on any porn sharing forum. Period.