Most insurance companies, when you get a diagnosis and you get treated at the place where your son is studying and after that he comes back to HK for a follow up, there's a high likelihood that it will get covered. But better you check with the insurance company.
AU Citizen, lived in Sydney for 18 years. left HK P.4 Term 1, 9 years old, studied in Sydney, attended USYD (Bachelor of Commerce) and UTS (Masters of Marketing). Now working in HK.