Interesting question, I hadn't thought about that before. Moderators are human beings, not robots. So, there will definitely be a time when they will never visit this forum again. I wonder, have the moderators in this forum ever been replaced by other user? Or have the current moderators never been replaced since they became moderators?
Nothing is irreplaceable, including the moderators of this forum, whether general admins or local moderators. I remember some members who previously aspired to join the forum's operating team, especially when not all local languages were supported. I also remember some moderators being changed or added, such as the famous Lauda, who I remember was a moderator before being replaced later for reasons that would take too long to explain. I also remember one of the moderators becoming inactive for a long time before the administration decided to replace him.
I don't know what prompted the OP to consider this issue, as I'm certain it's not a priority, especially since there are no vacant moderation positions on the forum's operating team.