Hmm, ok. So should I just get rid of the 'This message has been deleted'On the other hand, what about "undelete"? Is that a feature anyone wants? To have the feature there must be a way to find a placeholder for the message.
I ask because sometimes moderators would ask about undeleting messages mistakenly (or maliciously) deleted by another moderator. The typical scenario is a novice moderator who mistakes the Messages list for a kind of personal inbox and deletes messages as he/she reads them.
Groups.io is already in better condition than Yahoo Groups in that regard, having labeled the message archives "Archives". That helps imply that it is a group resource not a personal one, making the mistake less likely.
If there were to be an undelete capability, I would propose that when a member deletes their own message then either only that member can undelete it or no one can - not any moderator or owner in either case. That is necessary, I think, to preserve the promise that the member has the right to remove their content. Conversely if a moderator deletes a message only a moderator (not the posting member) can undelete it. This is necessary to preserve the right of the group management to control the content of the group.
On the other, other hand, if undelete is only available to moderators (when reversing another moderator's deletion) then the Activity log entry for the deletion event would be an appropriate place for an "Undo" button.