I think each case should be viewed differently.
As we know from the history of this forum, most banned members have failed through such topics to get forgiveness from the admin and a second chance at this forum.
However, in very rare cases, some banned members with the great support of the forum community managed to get forgiveness from the admin and their permaban was removed, based on their contribution and importance to the forum.
Based on that, I don't think moderators should be asked to remove such threads.
If a topic has the support of the forum community then it will survive and stay active for years, if needed.
Otherwise, if there is no support from the forum community, the topic will die naturally and there will be no need for any moderator intervention.
Useful topic are always helpful in the forum as they help to resolve some challenge entangled by other users. If a topic from a ban user is considered void the admin in due time have such topic mod and if it is considered good topic the mod then survive the post not to get deleted
