I worked with a sibling group of 5 (fostered, nearly adopted 2, was considered to adopt 2 more). Each child was SO-O-O different, even the identical twins! In many ways, the youngest 2 were the most severely affected, even though they were removed from the neglect/abuse at an earlier age. I am not sure how to separate the PTSD from the RAD symptoms, but all these kids had both diagnoses. My 2 settled into my family fairly well (extreme behaviors gradually mellowed, although no one would ever confuse them with "average" kids).They were returned to the bio-mom, and are maintaining fairly well, I hear. The twins were adopted by another family, and have continued to be very high needs.
I work with several families with kids with RAD, and see such a spectrum of effects. There seems to be no predicting which kids will heal, and which will not. My agency works with many trauma-affected kids (not all have RAD). I see little correlation between the severity of abuse (as far as I can glean from the sometimes sketchy histories) and the long-term outlook. Resilience seems to be the unpredictable factor, and not necessarily genetic (like the twins above).