I don't think not having an IEP in place when the school is doing all it can is ever a reason to not attend school. Of course, I don't know all the facts. What is it the parents want in place before their child goes to school? Is there a fear of elopement or some other safety issue? If so, that would be a valid reason, but have they asked the school to put something in place informally until the IEP can be put in place? Would a 504 (that process is usually faster) work until the IEP could be put in place? If there is a valid reason, have the parents asked for ways to instruct the child at home until they feel comfortable enough to send him/her?