I need ask someone who knows about hashimoto's thyroiditis. how long does the disorder last?

Lifetime: Hashimotos is an autoimmune disease where the immune system attacks the thyroid. It rarely resolves spontaneously. The typical case causes enlargement (or goiter) early on, then as the destruction of the thyroid progresses the thyroid slowly shrinks until it is very small later in life. Most patients will require lifelong thyroid supplementation.

Usually permanent: Hashimoto's thyroiditis is a condition where the body is making antibodies which destroy its own thyroid gland. Fortunately, it's very easily treated.