I agree with the home tutor option from the school district. I'm assuming that with his illness, it would be best to protect him from infections and things like the common cold that are prevalent in classrooms. And attending school can be tiring, too, when a child is dealing with an illness.
However, if his mom enrolled him in the public school, he might be able to get a tutor provided to him, and perhaps still enjoy an occasional trip or party or event as his health allowed. It would help him feel connected to the other students.
My daughter received homebound services for an entire year.
What it did for me, as her primary caregiver (of course, my husband was involved, but he was at work most of the time), was allow me to have a small break, knowing she was in capable hands with a certified teacher. Frankly, I did so much for her (taking her to appointments, doing her therapy exercises with her, preparing her meals - which involved avoiding restricted foods and making sure she was getting enough nutrients, keeping track of medications and records, going to the pharmacy, researching her diagnoses, talking with the insurance company, etc) that not having to allow plan lessons, teach, and grade homework was a bit of a relief for me.
She didn't have an IEP, because she didn't need any modification to the curriculum itself. She had a 504 plan which allowed for a reduced course load, and allowed for the tutor to come to our home.
Caregiving can be a full-time job, and taking advantage of every support option can be support for the patient, and support for the parent, too. Sometimes, kids who have serious illnesses see more of their doctors than they do other kids. My daughter enjoyed having the tutor come. Along with the schoolwork, the tutor visited with her a bit, and brought a bit of the outside world in.
If your cousin decides to ask for a home tutor, have her child's physician write a very specific letter. The letter doesn't have to reveal all the diagnoses, but it should say something like "[child's name] is under my care for an extended illness. [Child] should not attend regular classes in school, as he is at risk for infections and has reduced immunity due to medical treatments (or whatever the doctor feels is necessary). [Child] requires tutoring at home from a district-certified tutor for the entire school year of 2015-2016.". A similar statement can be obtained regarding any autism therapies or curriculum adjustments from the child's therapist. I found out that it was helpful for the physician to specifically state that home tutoring was necessary, and for him to state the duration that was required. The first letter we got just said that my daughter had illnesses and needed accommodations. It wasn't specific enough for the school. So a specific letter did the trick.
This way, if your cousin's child gets healthy enough to go to school (and hopefully that will happen!) he'll still be used to the idea of a teacher, and will be familiar with the school's curriculum.
Whichever way your cousin chooses to educate her child, I wish them the best on the journey.