If they do this again or you decide to go with a new plan, even though your policy will no longer be covering mental health and probably need it for your other medical anyway, just do not let it lapse before finding another and being covered by it. You cannot be subjected to a preexisting clause with the new policy if you get a "certificate of coverage" letter from your existing company which will help with the transition and ensure you do not get slammed without it, so instead existing diagnoses are covered with the new one.

Glad it was reinstated in the meantime. Good luck finding a new plan if you decide to do so!!