Hi there,
Whoever told you that you have to remain in treatment in order to maintain your rating was absolutely 100% mistaken. There is no such requirement. PTSD and other conditions that are not automatically considered premanent (like migraines) require follow up review examinations every 5 years regardless of whether you are in treatment. What happens to your rating depends largely on what information you disclose to the examiner during that follow up examination as well as any testing they perform. If the examiner has medical records to help them formulate their report, that is helpful, but it doesnt need to be 5 years worth and it isnt required.