I think the barrel extension actually cracked in half... That's what it looks like to me. It could probably be removed but I think you'd have to weld something onto it to get it off...
To the OP, the rifling won't ever "look" like it's degraded, the throat erosion is usually what kills the accuracy in a rifle.
Hammer forging, salt bath nitriding or hard chrome will all help reduce throat erosion as i put in my post.
The barrels I mentioned (Daniel Defense or FN) will have a full service life of between 20,00 and 30,000 rounds which means little or no accuracy degradation at that point. After that you will likely notice a very slow minor accuracy loss over the next few tens of thousands of rounds. It's possible to get 50,000 out of a barrel like that if you're not doing mag dumps and getting the barrel extremely hot (not as much of an issue with 5 or 10 round mags) and have it still be doing around 2moa or so. Which IMHO is a very reasonable accuracy level with such a high round count.
Look at what the Swiss Arms SIG550 is capable of doing in terms of longevity and accuracy, then realize it's a cold hammer forged barrel with a nitrided finish, just like Daniel Defense barrels.