Hi elizabeth4,
I have two friends who were in similar situations with similar sounding kids....and both now are very different kids now that they are HSing. It seemed so much of their issues were related to school. It's really quite shocking. I wouldn't beat yourself up over it. Now you know and can move forward! 8-)
About the DYS program, he doesn't need FS of 145, but rather 145 in either VCI or PRI indices.
About friends....are there any co-ops in your area? I find that for my son at least, having a few good friends is much better than have 20+ *friends* at school. Are there a few friends from school he'd like to keep up with? Can you schedule playtime w/ those kids? I would start searching out other HSers in your area and see if you find someone he connects with.
About re-entry into PS.....yes I've thought of this myself. Especially in math, I see him pulling further away from his peers. As well as in science and history. Composition...not so much lol.
My thought is that I really can only deal with right now. If I don't preserve his love of learning now, help him to learn to stick with it when the learning gets tough, then it doesn't matter what great school might be there in the future. I'm still not challenging him enough I'm afraid. I'm learning about HSing and learning about HIM as I go along. this is our first year HSing and my son is a 3rd grader by age.