Could symptoms of diabetes insipidus disappear and then return, why?

YES. Post brain surgery or trauma or irradiation or chemotherapy, can cause transient diabetes insipidus and siadh. Treatment is indicated during the transient phase.
It could. Recurrence of di after head trauma/surgery is not uncommon. It represents the final stage of the "tri phasic response" in which di takes place in the immediate post surgery/pituitary trauma followed by excess anti diuretic hormone state (SIADH) that can last from 5 days up to 2 weeks before entering a state of di again. Depending on the insult, di can be transient or permanent.
Depends on cause. Di comes in a central(brain)form and kidney form.Things that cause interruption of the di hormone production, release, storage, transport or kidney sensitivity can give di. Trauma around production areas, as might occur with brain surgery & an infection like encephalitis might produce a transient di that resolves as production returns to normal levels.