I am so sorry that you have to go through this with your son.
I too recall reading online about aplastic anemia and becoming depressed at what I found. However, much of what is online is out-of-date, and modern medicine is getting better at treating this in many ways.
I am 2 years post-ATG myself (my siblings were not a match, and I'm in my 40s, so immunosuppresant therapy was deemed the best 1st option), and doing pretty well. I've went from being greatly disabled by SAA, to working fulltime, exercising, taking my kids backpacking and skiing. I have my life back.
I can say that by far the hardest part of this disease has been psychological for me, the worry of the uncertainty. If only I had known 2 years ago at this time where I would be today - I wouldn't have suffered nearly so much! It is much easier said than done, but I would encourage you towards optimism in light of the treatment possibilities and advances, instead of worry at the uncertainty.
As sbk007 said, transplant in children has a very high success rate, and the doctors are getting better at it all the time. Also as sbk007 said, it is very important to be at a treatment center where the doctors are experts in aplastic anemia (or at least in close consultation with such a center), as this is such a rare and mysterious disease. You may have come across Dr. Neil Young of NIH in your reading. He has done very great work in treating aplastic anemia, and he strongly recommends this.
I'd like to share some other promising examples of recovery from SAA I know of.
There is a person in my support group who is an emergency room physician by trade. He had to go through two transplants to be cured, but he had his last transplant 10 years ago, and he is now cured for all intents and purposes. He works long shifts heading an ER, then finds time to go out X-C skiing on 20 mile stretches.
And that long battle he had to go through is usually not nearly as bad in younger folks. This same fellow had a classmate in medical school that got SAA as a 3 year old, well over 30 years ago now. He received a transplant from his twin sibling way back then, and completely recovered to live a normal healthy life, and go on to become a doctor himself.
A friend of mine has a similar story with his grandson 20 years ago, receiving a transplant from his non-twin sibling for leukemia. Twenty years later his grandson is a completely healthy young man.
And even if there is no sibling match, I understand some of the greatest advances are being made in the field of non-sibling transplants (MUD), even with less than perfect matches. Another person in my support group received a 9/10 MUD transplant last year after failing the ATG treatment. 10 months post-transplant, she is doing great. Her counts are near normal, she's tapering her meds. She feels immensely better than prior to transplant. She also works in medicine, and recently got back from a medical mission to Peru working in remote villages. And she is in her 40s.
And, if transplant is not the route taken, there are many people decades out from immunosuppressant treatment who are doing great. My son's teacher's husband received ATG for SAA over 25 years ago. He got better slowly, but he is recovered and his counts have been normal now for a quarter of a century.
While ATG does not always work and patients can relapse, promising research in other non-transplant treatments is being done. Here is one such example from Dr. Young and his colleagues:
When considering things to read online, I understand the AAMDS society & NIH recommends this as among the best overviews:
...and here is Dr. Young's most recent paper, combining info on conventional treatments with ongoing research:
So in short, while the initial diagnosis of SAA can sound horrible, with apparently few treatment options, I'm convinced the full picture is more promising than that, and looking better all the time.