Hi Dazzle,
A few things to remember (and really cling to) whenever you are searching for your crystal ball are:
ASD means a triad of imparement NOT an inability to learn, although some children may have other co-existing dx that affects this ability, many don't.
This means that even though NT social & communication methods are not their preferred methods they can be taught and LEARNED. Learned behaviour may not be completely natural but can become easier with practice over the years.
ASD is a spectrum, like a rainbow. You may find similar children on the spectrum but never exactly the same, if only for how they respond to therapy due to personality.
Therefore any, well meaning, experts who write these books can only write from their own experience and will often use the examples that really stuck in their minds. Milder or mid spectrum ASD children are often not noteworthy in these books.
Yes, you need to read up on ASD but more importantly you need to remember that your DC is an individual and the same loveable personality is stil there.
And I haven't yet met any sibling that gives up. Mine really enjoy each others company and genuinely love each other unconditionally. There really is no reason for you to expect anything else for yours.
I wholely agree with other posters here. You and your DH were the experts on your DS before the DX, you are the experts now and you will always be.
It's like climbing a mountain when you've never walked up a hill before. Seems impossible when you stand back and look at it yet one foot always follows the other anyhow.