This is genuine curiosity, is it possible for his anus to ever look normal again? Like a regular non-constantly fisting person's anus?
I've fisted some guys before and in each case their holes looked as normal and tight as anyone else's I've laid eyes on.
The anus actually has a surprising ability to stretch. Most people can take a small/regular sized fist, right of the bat, if they can get the muscles to relax enough. There isn't really anything special to it.
Getting fucked doesn't do anything to actually stretch you either unless the guy has one of the thickest cocks on the planet. I mean if most people can actually take a fist then taking a cock is getting nowhere near the limit of how much the skin can stretch to. Just think of all the bottoms that get DPd every once in a while. Of the ones that I know they aren't doing anything to prepare for it they just can because the anus can stretch that far.
All that happens when a guy gets 'good' at taking cock is that he gets good at learning how to relax on demand. So instead of it taking a couple of minutes for him to open up it takes seconds.
In my experience most people say 'busted hole' and words to that effect when a hole looks relaxed, open, and puffy. Puffy isn't usually caused by the skin or muscle. Puffy is from swelling and enhanced appearance of the other tissues that are a part of the anus. This is mostly from the blood vessels. Usually the ones in the anus have a very poor blood supply due to being tightly squeezed shut by the anus muscles. But if you relax enough for a while they will become filled with blood. Also if you're getting fucked hard every day this will also cause a degree of general inflammation as the tissues increase blood flow just from being worked on.
The extra swelling from this is completely reversible.
The only way you're going to get extra skin and muscle growth is if you're constantly inserting objects right up to your stretch limit and then keeping that object in so you're holding yourself stretched open.
This is not a quick process. Those that enlarge there foreskins, to cure phimosis, spend months with daily stretching routines. And it's the same with those that enlarge their earlobes piercing holes.
I think it's actually far more common for guys to appear to have a busted hole if they suffer from a degree of chronic haemorrhoids or anal fissures. The body constantly tries to heal them leading to a naturally puffy appearance when you've ever even taken a fist.