A health insurance policy in India is more or less hospitalisation reimbursement policy. It covers health risk where person needs to be hospitalised for some specific duration in the hospital.
Hence Cancer, heart ailment where patient will be operated in the hospital is covered under such policy.
But in few cases like cancer, diabetes where one needs to have more expenses on OPD (out patient basis are not covered).
Such expenses can be covered with plans being offered by few Life Insurance companies. They are unit linked plans. It's always better to start with traditional health insurance policy and then take other policies.