You don't have to be dwelling on it now. When the time comes, he'll go to school and, even if he is upset at school, he will calm down once you leave. By all means do not indicate to him that there is any alternative to his attending school. If it's not a major problem for you re: logistics or schedule, it's fine if he doesn't take the bus. But you are certainly correct in thinking that he may well have a problem leaving you once he's at school. Work cooperatively with the staff at school. They are used to such examples of anxiety and will help him to separate from you. Be sure not to linger at the school. Bring him to his teacher and leave.
I wouldn't worry about it now....although what I tried to do is schedule an appointment to see the classroom and teacher so at least it's not like they are walking into a totally new atmosphere. And they will be a little more familiar with the teacher and hopefully the school will make a good match for your child with a good teacher if they know some of the issues you deal with. That's just my hope for my child...I don't even know if it's possible to chose a teacher.
Good Luck!
I just couldn't do that to my child. When they hit Kindergarten I guess we really don't have much of a choice. But I would try and meet the teacher and I'm sure the teacher and school staff will reassure you.