I was told that once your thyroid fails lifelong medication is required. I guess there are cases of thyroiditis that will correct itself, but most cases of hypothyroidism require medication forever.
My grandmother was treated for hypothyroidism in the 60's. They took her off the medication and never checked her levels again. She eventually developed severe dementia that her geriatric Dr. attributed to untreated hypothyroidism. If you can, the best Dr. to see for this condition is an endocrinologist. They specialize in metabolic disorders.