Tag Synonyms vs Target Tag Deletion: What Happens When the Target Tag Is Removed?

Background

Stack Overflow’s tag‑synonym system lets high‑reputation users propose a mapping from a source tag to a target tag. Once a synonym gains enough votes, the source tag is hidden and any post using it is automatically relabeled with the target tag.

Unresolved Behavior

There is no documented policy for how the system reacts if the target tag is subsequently deleted, merged, or otherwise removed from the namespace. Observations suggest that the synonym record may persist, leaving an orphaned entry that no longer resolves to a valid tag.

Questions for Clarification

• When a target tag of an accepted synonym is deleted, does the synonym entry automatically disappear or remain in the system?
• If the target tag is merged into another tag, how does the synonym mapping update—does it redirect to the new target or become inactive?
• Are moderators able to delete or edit such orphaned synonym records, and does the system enforce any consistency checks during that process?