I feel for you devientenigma, your DS has very very complex needs indeed and I can imagine you being physically and emotionally exhausted with having little or no respite at all from meeting his daily needs ( you dont say what family / care at home package you have.) never mind trying to plan for the future.
I agree with others that in reality the local school itself cannot do anything about physically getting your son to school ..... and by the sounds of it there has been a fair bit of support via other agencies to try and enable this to happen with the provision of adults / transport in the morning to support you. As others have said if he is so unwilling to go they cannot physically force him into the bus.
It is a shame he feels afraid. ...and it may be something very "simple" or it may be something serious but whatever it is it is serious to him .....and may or mot be able to be remedied for him.
While it is wonderful to think that every person can be supported to stay with their family sometimes it can actually prevent a complete breakdown (individuals physically / mentally and / or of the family relationships) if the YP moves into specialised residential setting. Its not a perfect solution but life is not perfect, we all just do the best we can to make it as good as it can get.
I have often seen both the children and the family flourish when this has happened in my professional life as well as my personal life. Some parents and siblings have been able to live in less fear of injury, be able to sleep at night and begin to make a better relationship with the child with the complex needs. My friend no longer gets used as punchbag if she does not give her son exactly what he wants when he wants it ( whether thats day or night) and he is developing a life with people his own age (and where DM and siblings can visit).
There are not that many residential schools and they often take children in from very, very wide catchement areas.
So what would you like to happen in an ideal world ? I think only then can you really fight for whatever you need to have to make it happen.
Take care of yourself.