I don’t think I understand? Are you somehow able to see what the post was?
Yes, moderators can do that. They can also see what the text was like before you edit it.
Is there a time limit beyond which a user no longer has the option of deleting a post? And if so, what is that limit? And if not, WHY THE FUCK NOT?
Also, if I delete a post, and have second thoughts about the deletion, can I UNdelete it? Are there limitations on THAT?
Right now, it looks like there’s no limit. I went back to a thread I started in 2015 and the option was there.
Yes, I did the same, and found the option open to me. I didn’t click it, though (because I don’t know if I could reverse it. It might just flip me the bird, and tell me it’s after the bell, mate).
Nope. No way to undelete it.
Are there any management guidelines on the use of this feature? Given it’s possible, is it considered bad form or something?
Yes there is. 
Showoff. 
I think there is a time limit on it. We would prefer it if you basically follow what we had on the old software. You could “delete” a post in vBulletin by editing it to say never mind or something similar within the 5 minute edit window. Stick with that (ok to delete it within 5 minutes) and we don’t have a problem with it.