Free T4 and T3 have normalized after 2 weeks on methimazole, but TSH is undetectable. Normal cortisol and pituitary. Could TSH still normalize?

Could. It is not feasible to give you the odds of a permanent remission. It would be prudent to follow your doctor's directions for medication and visits.
Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.
Practice safe sex, if you have sex.