A.S.
Yikes, I see you're in Texas. You might want to read some of TracyXO's posts (pertaining to a truancy fiasco) before you decide how to proceed.
I would also review the school handbook.
I don't put up with schools and their increasingly ridiculous, arbitrary (based on getting federal funding $$$) rules, which is one reason (among many) why we homeschool. That being said, if you're in their system you generally have to play by their rules.
Good luck - I think trips are great learning experiences for kids. And I agree that it's very difficult for ASD kids to tolerate lines, and heat too. Also, you might contact WDW and see if you can get a special pass or accommodation.