Although anecdotal, I have had two back injuries. One from shrugs and my most recent one from shoveling dirt for 3-4 hours straight and making wheel barrel runs. Back injuries, if they are not muscle related take a very long time to heal. I think people become impatient and quit doing what they should be doing.
The first time I seriously inured it, I rested my back thinking rest was the way to go. Problem is, my back continued to get worse. After 3 months of a chiropractor and still my back degenerating, I decided to hit the barbells again. As I lifted what what my back could handle, I noticed it getting better and better. Within another two months, I was pain free and about 6 months later I worked up to a 435 Deadlift @ 180 in weight. My back was better than new, or at least back to where it was.
What I find interesting that even a very strong back can be injured doing something as simple as shoveling dirt. Granted, I was shoveling huge loads of clay and taking huge wheel barrels of dirt and dumping them, I eventually hurt my back. This time, it was a bulging disc. It only hurt when I did certain movements. I could avoid any pain by avoid shoveling (bending of the back) and by avoiding squats. At first I had no idea it was a bulging disc, so I treated it like a muscle belly injury and did very light rounded back exercises... Problem is, it never got better. It always stayed the same. I figured out the rounded of the back in that way, especially with weight, although minor is the same exact position that shoveling puts your back in often and was contributing the bulging disc. Once I learned that, I studied up on sheer force and while I already knew proper form to lift with, I never truly understand the bio-mechanics of sheer force until I studied them closely. Once I identified the problem, I started a new regimen which was:
* No Deadlifting
* No Squatting
* No Shoveling
* Standing as much as I could rather than sitting as that kept my spine neutral.
After about 3 months of that the pain was gold. I tested the waters carefully and am now able to do quick lifts again like the Power Clean or speed deadlifts. Deadlifting is back up to 365. I still have a ways to go, but I have learned some very valuable things when dealing with the back.
For a summary - in both cases I had thought my back will never heal. In both cases the therapy was different. In both cases it took a very long time. 5 months for the first injury to heal and over 1 year for my second injury to heal.
Knowing what I know now, I could have cut down the recovery time to 2 months and 6 months respectively.
I personally believe most back injuries can heal on their own if treated properly. I think to many people get an injury and consign themselves to that injury for the rest of their lives. I am not saying every back injury can heal on its own, but the body is remarkable at healing once we stop doing things that cause the problem and allow it the proper stimulus to heal itself.
One more comment - I grew up under the Olympic lifts and was taught proper form. Neither of these injuries were due to form perse, but they were due to over zealous lifting and shoveling. Even those who know how to lift properly and still susceptible to back injuries and karma has a way to deal with people. Up until 30 I never back a back injury and I believed it was become I was superior, knew the right form and, yada yada yada. The first one was a humbling experience and the second one was a learning experience. I hope no one has to injure their back, but if so, I don't think it is that dire.
Edit **
Bill Starr's therapy worked for my first injury and aggravated and made worse my second injury. That is one way to determine if an injury is muscle related or not. If it is, it will always (or nearly always) benefit from Bill Starr's therapy.
http://billstarrr.blogspot.com/2012/01/rehabbing-lower-back.html
But related to the OP's title "Can a herniate disc heal itself?" Not sure. I know a bulging disc can. Some say it can, and I tend to believe it can... Neat site to check out.
http://breakingmuscle.com/mobility-...c-bulges-they-are-not-forever-but-training-is
There is some deviation from what is considering bulged vs torn... Sometimes they are used interchangeably.