Public school must be funded until 21 for anyone with a need for that. If a school can’t meet the kid’s needs, they must fund a least restrictive alternative (IDEA and similar laws). Within that funding, it’s incumbent upon the school district to ensure the placement is not going to cause harm/be unsafe.
In terms of the break, I don’t see anything that says they wouldn’t just take a couple short bike trips in that time span. Given the level of disability, it seems unlikely he’d go on a long bike trip. More likely they’d just take some day trips. This second paragraph is subjective and based on my work experience with similar families in the disability world.