It seems that the system still deletes a post by timer if the post was deleted by the user, even when a moderator has reverted this to the original post (so undelete it, to prevent a confusing topic).
Post was deleted by user, but moderator reverted this to the original post:
After 24 hours the post is deleted by system:
Hi @Albertos 
I’m giving this a run-through on my test site and I think I can replicate this:
delete removed posts after admin setting to 1 (optional, but saves waiting a day )
However, I don’t think that method actually removes the delete timer on it as you’ve not actually undeleted it in the same way as if the user had used the ‘undo’ icon (which is not available to admins without impersonating).
From a practical perspective, I’m not sure under what circumstances a moderator would want to undelete a topic that the OP has marked for deletion? A user can only delete a topic which hasn’t received any replies, so there wouldn’t be any conversation lost?
Hi @JammyDodger, thanks for checking!
In this case it was a post in the middle of a topic conversation. Without that post the conversation becomes a bit unclear to users who can’t see that a post has been deleted in between. Since there was no real reason for the user to delete that post, I decided to revert it to the original post.
Or maybe the post was the last, but another user was already replying. Not sure about that.
Aaahh. Faulty assumption on my part. I’ll have another go. 
I gave it a second run but with a post this time just to be thorough and got a similar result.
I think the mechanics are similar in that reverting the edit simply changes the content text and doesn’t affect the delete timer in any way, which I think is the way it is intended to work.
To avoid having to come back and undelete the post after the timer has run, as a moderator/admin you can delete the post there and then and then use the undelete option to bring it back. This restores the post and removes the timer.
However, allowing users to delete their own posts will sometimes leave topics with some holes in, and I’m not sure there’s any way around that bar removing the ability for a user to self-delete their posts? If that’s a more appealing option for your site you can amend either max deletions per day or max post deletions per minute to zero to disable user deletions.
I’ve slipped this over to support. 